Potts Drill Grinding Jig
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The following is a link to the jig I am asking about.
http://www.hemingwaykits.com/acatalog/The_Potts_Drill_Grinding_Jig.html
I have trawled the web and asked the same question in another forum and all I have found is scant mention of it working well and a couple that have had difficulties with it without finding out why.
I am in need of an accurate drill sharpening jig at a reasonable cost (in both time to build and money terms) and have dismissed most of the alternatives.
1. I have had one of the jigs that swing the drill on the edge of the wheel and they are useless IMO. (the type shown here: http://www.machinemart.co.uk/shop/product/details/dga1-drill-grinding-attachment)
This is probably due to a combination of making a poor copy of an original design and making it even worse by poor manufacturing.
2. Buying a Drill Doctor, this was high on the list and about as much as I would want to spend but I have been put off by reports of its use. About 50% say its OK and the other 50% say it is not and I am not willing to take a chance with those odds.
3. Making a clone of the swing type jig but designing out some of the problems with the cheap commercial versions.
(this may still be a fallback option)
The option is still open of making making the Potts as someone has already done the design work and a set of castings are available to ease constuction but I would like a bit more assurance that it will work well.
(BTW I have dismissed any thing that is a plastic attachment to an electric drill and yes I can hand sharpen the larger drills but I am looking for something to cover 3 to 12mm or so)
If any one has any suggestions that will help me make a desicion it would be appreciated
The following is a link to the jig I am asking about.
http://www.hemingwaykits.com/acatalog/The_Potts_Drill_Grinding_Jig.html
I have trawled the web and asked the same question in another forum and all I have found is scant mention of it working well and a couple that have had difficulties with it without finding out why.
I am in need of an accurate drill sharpening jig at a reasonable cost (in both time to build and money terms) and have dismissed most of the alternatives.
1. I have had one of the jigs that swing the drill on the edge of the wheel and they are useless IMO. (the type shown here: http://www.machinemart.co.uk/shop/product/details/dga1-drill-grinding-attachment)
This is probably due to a combination of making a poor copy of an original design and making it even worse by poor manufacturing.
2. Buying a Drill Doctor, this was high on the list and about as much as I would want to spend but I have been put off by reports of its use. About 50% say its OK and the other 50% say it is not and I am not willing to take a chance with those odds.
3. Making a clone of the swing type jig but designing out some of the problems with the cheap commercial versions.
(this may still be a fallback option)
The option is still open of making making the Potts as someone has already done the design work and a set of castings are available to ease constuction but I would like a bit more assurance that it will work well.
(BTW I have dismissed any thing that is a plastic attachment to an electric drill and yes I can hand sharpen the larger drills but I am looking for something to cover 3 to 12mm or so)
If any one has any suggestions that will help me make a desicion it would be appreciated
I don't know anything about the Potts jig at all, but I will talk to you because no one else has, and hopefully give you a few pointers from the outside.
I occasionally use one of the cheapo plastic ones that fit onto an electric drill (Martek, I think), but I have made mine a bit more rigid by giving it it's own dedicated small motor, and it really works surprisingly well on the larger sized drills, but forget about anything under about 6mm.
With regards to the Hemingway Potts jig.
They always make out things are easier if made from castings, but I have invariably found that castings make a lot of extra work, purely because they don't have any datums to start off with. I have worked out that working from barstock, where you have datums from the very beginning, and if you are capable of producing the shapes by manual means, is always the best way to go. Even if it means fabricating some bits with say silver solder or welding, or even bolting together.
If you look at the end of the description by Hemingway, it does state that getting all the angles correct is really the main issue.
I am sure that if you searched about on the web for an hour or so, you should be able to come up with some design made from scratch that will allow you to achieve all that you require. I looked at this a few years ago, and even then there was a fair amount about, but then decided I just couldn't be bothered, and because of the low prices, I just replace most of my drills each year.
In a production workshop, they will most probably have a rather expensive dedicated drill sharpener, with all the cams to regrind almost any shape and sized drill, including four facet, slocombe, counterbore etc, but in that environment it would justify the large cost involved (you can sometimes pick them up second hand, but very rarely single phase). In our shops, you have to look at whether the costs to resharpen outweigh the costs to buy new drills. In my situation, I have found that buying in bulk for normally used sizes (very cheap) outweighs the time it would take me to resharpen the drills that go blunt.
I have shown this link many times before, and would suit the UK buyer, especially the metric ground ones.
http://www.leofixings.com/fixings_Drill+Bits-10.html
Don't let me put you off making a unit if that is the way you want to go, everyone to his own. I have just expressed my views looking from the outside.
Bogs
I occasionally use one of the cheapo plastic ones that fit onto an electric drill (Martek, I think), but I have made mine a bit more rigid by giving it it's own dedicated small motor, and it really works surprisingly well on the larger sized drills, but forget about anything under about 6mm.
With regards to the Hemingway Potts jig.
They always make out things are easier if made from castings, but I have invariably found that castings make a lot of extra work, purely because they don't have any datums to start off with. I have worked out that working from barstock, where you have datums from the very beginning, and if you are capable of producing the shapes by manual means, is always the best way to go. Even if it means fabricating some bits with say silver solder or welding, or even bolting together.
If you look at the end of the description by Hemingway, it does state that getting all the angles correct is really the main issue.
I am sure that if you searched about on the web for an hour or so, you should be able to come up with some design made from scratch that will allow you to achieve all that you require. I looked at this a few years ago, and even then there was a fair amount about, but then decided I just couldn't be bothered, and because of the low prices, I just replace most of my drills each year.
In a production workshop, they will most probably have a rather expensive dedicated drill sharpener, with all the cams to regrind almost any shape and sized drill, including four facet, slocombe, counterbore etc, but in that environment it would justify the large cost involved (you can sometimes pick them up second hand, but very rarely single phase). In our shops, you have to look at whether the costs to resharpen outweigh the costs to buy new drills. In my situation, I have found that buying in bulk for normally used sizes (very cheap) outweighs the time it would take me to resharpen the drills that go blunt.
I have shown this link many times before, and would suit the UK buyer, especially the metric ground ones.
http://www.leofixings.com/fixings_Drill+Bits-10.html
Don't let me put you off making a unit if that is the way you want to go, everyone to his own. I have just expressed my views looking from the outside.
Bogs
Tin Falcon
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Jim :
I do not think the pots design is well known. I for one do not recall hearing of it. Much less having experience with it.
I did google but did n ot feel that in in of itself warranted an answer.
I do have one of these I picked up new old stock from a thrift store
these are a production pot metal cast unit . Craftman also has/ had there own version. to be honest it is still new in box. I need to mount it one of these days.
I do use my drill doctor 500 . this is the older version before the improved x version. Most of the time i touch up by hand.
I am glad bogs chimed in here.
OK jim now that reread you post . I will say the older drill doctor does require a but of patience an finesse and feel to get good results. I guess you would call it a machinist touch. If you go in with with the finesse and brains of a gorilla you will ruin drill bits.
Also the new version has improved the machine and dealt with the short commings.
Hope you find something you are happy with.
Tin
I do not think the pots design is well known. I for one do not recall hearing of it. Much less having experience with it.
I did google but did n ot feel that in in of itself warranted an answer.
I do have one of these I picked up new old stock from a thrift store
these are a production pot metal cast unit . Craftman also has/ had there own version. to be honest it is still new in box. I need to mount it one of these days.
I do use my drill doctor 500 . this is the older version before the improved x version. Most of the time i touch up by hand.
I am glad bogs chimed in here.
OK jim now that reread you post . I will say the older drill doctor does require a but of patience an finesse and feel to get good results. I guess you would call it a machinist touch. If you go in with with the finesse and brains of a gorilla you will ruin drill bits.
Also the new version has improved the machine and dealt with the short commings.
Hope you find something you are happy with.
Tin
DICKEYBIRD
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Have a look here: http://www.gadgetbuilder.com/DrillSharp.html
John Moran is a good communicator and has "been there, done that" with exactly what you are seeking to do. No Potts jig info but a lot of good drill sharpening data. Have a look at his other stuff as well.
John Moran is a good communicator and has "been there, done that" with exactly what you are seeking to do. No Potts jig info but a lot of good drill sharpening data. Have a look at his other stuff as well.
Oh well as no one else has come forward re the Potts, i shall jump in.
I have a set of castings for the Potts and have got them about half finished, the easy half by the way. There, at the time of purchase, were no instructions on how to make the thing properly. I have to say that I had the first set and there was a suggestion that if I wanted to I could do the write up. So far the offer has been declined. Just had a horrible thought, it is now two years since I bought the castings at the Midlands Exhibition, must get around to finishing them.
As stated, the castings do need to be accurately made which is not that easy without something to copy, the drawings are good but as Bogs has said it is a question of Datums or lack of them.
Now to the jig, I am told that it works and if I do finish, sorry when I finish it and find that it does I shall spread the word.
Now, did you know there is another jig of the same basic design but made to be constructed from "barstock" as they like to call it on the other side of the pond. It was serialized in ME in late 1951 under the penmanship of "Duplex". This jig is also similar to the "Van Royen" but this just complicates matters. Dig out ME and have a look it will be much cheaper than a set of castings, but maybe not as pretty.
There is yet another option if you have a Worden T&C grinder, or with a bit of playing around a disc and belt sander. This is a four facet jig designed by Giles Parkes, yes he of gear cutting fame, to fit the Worden and is like all the best ideas very simple. The write up was in MEW a few years ago. When my Tuit list shrinks a bit, that is on my list.
Ned
PS I forgot to say why the Potts is supposed to be so clever, the back-off is altered by use of a built in caliper which measures the drill diameter and automatically adjusts the back -off. Clever huh!
I have a set of castings for the Potts and have got them about half finished, the easy half by the way. There, at the time of purchase, were no instructions on how to make the thing properly. I have to say that I had the first set and there was a suggestion that if I wanted to I could do the write up. So far the offer has been declined. Just had a horrible thought, it is now two years since I bought the castings at the Midlands Exhibition, must get around to finishing them.
As stated, the castings do need to be accurately made which is not that easy without something to copy, the drawings are good but as Bogs has said it is a question of Datums or lack of them.
Now to the jig, I am told that it works and if I do finish, sorry when I finish it and find that it does I shall spread the word.
Now, did you know there is another jig of the same basic design but made to be constructed from "barstock" as they like to call it on the other side of the pond. It was serialized in ME in late 1951 under the penmanship of "Duplex". This jig is also similar to the "Van Royen" but this just complicates matters. Dig out ME and have a look it will be much cheaper than a set of castings, but maybe not as pretty.
There is yet another option if you have a Worden T&C grinder, or with a bit of playing around a disc and belt sander. This is a four facet jig designed by Giles Parkes, yes he of gear cutting fame, to fit the Worden and is like all the best ideas very simple. The write up was in MEW a few years ago. When my Tuit list shrinks a bit, that is on my list.
Ned
PS I forgot to say why the Potts is supposed to be so clever, the back-off is altered by use of a built in caliper which measures the drill diameter and automatically adjusts the back -off. Clever huh!
jmshep, Book 38 in the "WORKSHOP PRACTICE SERIES" "TOOL AND CUTTER SHARPENING" by Harold Hall
has among many other things, a whole chapter dedicated to the jig shown above by
Tin Falcon.
Harold descibes in detail with drawings, a couple of simple mods which make the jig
quite usable.
He then descibes in great detail with drawings, how to use the jig for the best results.
There is a lot of good info in this book.
ISBN-13:979-185486-241-9
ISBN- 1-85486-241-3
has among many other things, a whole chapter dedicated to the jig shown above by
Tin Falcon.
Harold descibes in detail with drawings, a couple of simple mods which make the jig
quite usable.
He then descibes in great detail with drawings, how to use the jig for the best results.
There is a lot of good info in this book.
ISBN-13:979-185486-241-9
ISBN- 1-85486-241-3
Thanks to you all for you replies I now have some other choices to explore and perhaps revisit.
Miker
You are right the book by Harold Hall is very good and I have made both the grinding rest (with some modifications such as addition of gib strips, mounting brackets etc) and the 4 facet drill grinding jig from it. The 4 facet jig works well for meon drill above about 6mm dia but I still need to be able to grind drills conventionally.
Alas the modifications and explanation of the 'swing' jig' did not work for me as the thing was incapable of providing the correct geometry in the first place. I tried all combinations of lip angle and dill protrusion and in each case the relief angle was too large. I think the problem may lie in the amount the V is offset from the pivot but the tool is really is not worth further investigation because of its poor quality. If I were to make a clone I would make this feature adjustable so that it can be determined by trial and error as I do not have enough understanding of the theoretical geometry involved to design one on paper first.
Regards John
Miker
You are right the book by Harold Hall is very good and I have made both the grinding rest (with some modifications such as addition of gib strips, mounting brackets etc) and the 4 facet drill grinding jig from it. The 4 facet jig works well for meon drill above about 6mm dia but I still need to be able to grind drills conventionally.
Alas the modifications and explanation of the 'swing' jig' did not work for me as the thing was incapable of providing the correct geometry in the first place. I tried all combinations of lip angle and dill protrusion and in each case the relief angle was too large. I think the problem may lie in the amount the V is offset from the pivot but the tool is really is not worth further investigation because of its poor quality. If I were to make a clone I would make this feature adjustable so that it can be determined by trial and error as I do not have enough understanding of the theoretical geometry involved to design one on paper first.
Regards John
Tin, I had the craftsmen jig you show in the picture for about a week. It works somewhat, the relief must be done by hand. I took it back to Sears as I did not care for it. I can grind as good by hand as the jig does.
Several years later I bought the least expensive Drill doctor from HD for $35.00 (#300 model) on sale.This is the original model, I have not used the new and improved model.
I am very happy with it. I spent a couple of hours practicing ,watching the video and reading the instructions,My machine sharpens drills from 3/32" to 3/8". I have sharpened numbered bits down to #51. The smaller bits are a crapshoot,I only get it right about 75% of the time. The manual says 3/32" is the smallest it will sharpen but I still try any bit that is dull.
I have been using it quite a bit for the last three years with no complaints.The learning curve is short, I got better after ruining the same drill many times. After a dozen or so sharpenings I got the hang of it. If a bit is broken, I grind freehand and the the drill doctor.
mike
Several years later I bought the least expensive Drill doctor from HD for $35.00 (#300 model) on sale.This is the original model, I have not used the new and improved model.
I am very happy with it. I spent a couple of hours practicing ,watching the video and reading the instructions,My machine sharpens drills from 3/32" to 3/8". I have sharpened numbered bits down to #51. The smaller bits are a crapshoot,I only get it right about 75% of the time. The manual says 3/32" is the smallest it will sharpen but I still try any bit that is dull.
I have been using it quite a bit for the last three years with no complaints.The learning curve is short, I got better after ruining the same drill many times. After a dozen or so sharpenings I got the hang of it. If a bit is broken, I grind freehand and the the drill doctor.
mike
Hi, JMSHEP
I purchased the parts for this jig from Hemingway Kits a couple of years ago. The kit included 6 iron castings and 1 gunmetal casting, together with all necessary bar materials and fasteners. The iron castings were good quality, free from blow holes and hard spots. The accompanying drawing is comprehensive.
I did not take photos of the build but it was pretty straightforward until it came to machining the upper drill platform (the piece with the long slot which holds the slider block and 'V' rest for the drill being ground - Item 4 on Hemingway drawing). This had a slight bow in its length but there was enough material to mill both sides to size and get rid of the bow. I attached a magnetic table to the milling machine and milled the platform with suitable packing under the void. It was then turned over and finished to size. Using this method, the article must be restrained from movement in a horizontal plain using the fences provided and additional pieces of steel plate on the magnetic table for security. Obviously this could be machined directly on the milling machine table using clamps, etc., although care would be required not to induce further abnormalities in the casting.
The jig is worth making. I set it up on my 8" grinder and proceeded to attack my using drills 1/8" - 1/2". It made a superb job of them. I used to grind them by eye and they were passable but this is the dogs b----cks.
Hope this is of some help.
Ed
I purchased the parts for this jig from Hemingway Kits a couple of years ago. The kit included 6 iron castings and 1 gunmetal casting, together with all necessary bar materials and fasteners. The iron castings were good quality, free from blow holes and hard spots. The accompanying drawing is comprehensive.
I did not take photos of the build but it was pretty straightforward until it came to machining the upper drill platform (the piece with the long slot which holds the slider block and 'V' rest for the drill being ground - Item 4 on Hemingway drawing). This had a slight bow in its length but there was enough material to mill both sides to size and get rid of the bow. I attached a magnetic table to the milling machine and milled the platform with suitable packing under the void. It was then turned over and finished to size. Using this method, the article must be restrained from movement in a horizontal plain using the fences provided and additional pieces of steel plate on the magnetic table for security. Obviously this could be machined directly on the milling machine table using clamps, etc., although care would be required not to induce further abnormalities in the casting.
The jig is worth making. I set it up on my 8" grinder and proceeded to attack my using drills 1/8" - 1/2". It made a superb job of them. I used to grind them by eye and they were passable but this is the dogs b----cks.
Hope this is of some help.
Ed
I was VERY skeptical about The Drill Doctor units being of any practical use but after a friend of mine brought his over and let me 'play' with it for about a week, I'm here to tell you they work as advertised. Normally I grind bits by hand and am reasonably adept at the practice as the old timer that taught me in college made us practice the art for 1 hour every other day in class and the motions have stayed with me all these years. The DD however takes all of the guess work out of the equation and once the bit is set up in the carrier properly, it does the rest. A few turns of the preformed carrier, applying a light touch on the diamond wheel , and you have yourself a perfectly ground cutting edge. I spent an entire day grinding every bit I had in the shop that would fit the thing and was amazed at the performance difference afterward. I would highly recommend them to anyone, even if they are around $100. Christmas is coming you know.
BC1
Jim
BC1
Jim
Well
Thanks for the last two posts in particular and now I still have a decision to make - Build a Potts from the Hemingway kit or buy a Drill Doctor.
I had almost dismissed the Drill Doctor but comments about more recent models seem much better than those of the older ones. Taking time and materials into account the cost is probably not much different but I probably favour the Potts if only for the satisfaction of making it myself now I know it works.
John Shepherd
Thanks for the last two posts in particular and now I still have a decision to make - Build a Potts from the Hemingway kit or buy a Drill Doctor.
I had almost dismissed the Drill Doctor but comments about more recent models seem much better than those of the older ones. Taking time and materials into account the cost is probably not much different but I probably favour the Potts if only for the satisfaction of making it myself now I know it works.
John Shepherd
Hi Guys,
This side of the pond the Drill Doctor is considerably more expensive than you chaps have to pay. The DD750X is listed at £214.57+VAT(soon to be 20% instead of present 17.5%) in the MSC/J&L catalogue. The US Ebay seller is asking less than £90 for the same thing but will not supply the 240V model.
Apparently the reason it is so much more expensive over here is "because it is special being 240volt not 120V"
Makes you want to *bang*
Ned
This side of the pond the Drill Doctor is considerably more expensive than you chaps have to pay. The DD750X is listed at £214.57+VAT(soon to be 20% instead of present 17.5%) in the MSC/J&L catalogue. The US Ebay seller is asking less than £90 for the same thing but will not supply the 240V model.
Apparently the reason it is so much more expensive over here is "because it is special being 240volt not 120V"
Makes you want to *bang*
Ned
For that sort of money Ned, you can buy hell of a lot of drills, or it could go a long way towards a second hand Alexander tool & cutter grinder.
Bogs
Bogs
Hi all, just discovered this thread or I would have jumped in earlier. Drill sharpening jigs, I have one (was curious) and have only had a couple of minutes play with it. Not even sure of its title, it is probably 15 years old.
Reason I piped up, unless you are sharpening dozens of bits per day..... learn to hand sharpen your bits, no expensive machinery and along the way you can also learn to 'modify' for one off applications.
I did a 10 year stint as a trade teacher (automotive) but I always ensured my first year students COULD sharpen a dril bit.
Having said that, below 6mm gets replaced and I buy them in packs of 10, but to be honest, I rarely have to replace them. I think this is beacuse of a something I call 'mechanical sympathy' I try not to abuse tools, by understanding what they can and cannot do, and also having a 'feel' for when a cutter is labouring or just doesnt feel right.
Sharpening a drill bit is a very hard to learn by reading about, it needs lots of demonstration and practise.... its worth it if you can find and old stager to show you....
Ok, off my soap box... 8) I know, I know..... but non hand sharpening of drill bits is my pet hate ;D and we all can do it.
Reason I piped up, unless you are sharpening dozens of bits per day..... learn to hand sharpen your bits, no expensive machinery and along the way you can also learn to 'modify' for one off applications.
I did a 10 year stint as a trade teacher (automotive) but I always ensured my first year students COULD sharpen a dril bit.
Having said that, below 6mm gets replaced and I buy them in packs of 10, but to be honest, I rarely have to replace them. I think this is beacuse of a something I call 'mechanical sympathy' I try not to abuse tools, by understanding what they can and cannot do, and also having a 'feel' for when a cutter is labouring or just doesnt feel right.
Sharpening a drill bit is a very hard to learn by reading about, it needs lots of demonstration and practise.... its worth it if you can find and old stager to show you....
Ok, off my soap box... 8) I know, I know..... but non hand sharpening of drill bits is my pet hate ;D and we all can do it.
I can't help with the Potts grinder, but have used the simpler pot metal one. It worked fine, when you managed to get the little finger that locates on the drill flute adjusted correctly and the stick out from the end of the jig right (this controls the clearance angle of the cutting edge).
Learning to grind by hand is an acquired skill. Think of the drill inserted in the hole it has just made. The chisel point will be resting on a small flat circle, the cutting edges will be resting on the cone at the bottom. Now envisage what is needed from the sharpening to make the drill cut. It needs clearance behind the cutting edge, just as a turning or parting tool needs clearance to cut properly, and that is what you do when you grind the drill. It is like creating a fine feed corkscrew.
The chisel point is just that, a rotary chisel, it is an inefficient cutter of metal.
No hand ground drill will be perfect, it just can't be done, but you can get it near enough so that :-
It cuts easily (get the clearance right).
It cuts size (get both cutting edges the same angle and length).
Get the above right and the chisel point angle, looking at the end of the drill, will be correct.
Teenut posted a very good description on the rec.crafts.metalworking newsgroup years ago that some people swear by. It might be worth looking it up, it is a good tribute to remember Robert Bairstow.
I have old hands now but they can still remember the swing action that gets even a 1/16" drill ground right, even if I have to use a loupe to see the end properly!
IanR
Learning to grind by hand is an acquired skill. Think of the drill inserted in the hole it has just made. The chisel point will be resting on a small flat circle, the cutting edges will be resting on the cone at the bottom. Now envisage what is needed from the sharpening to make the drill cut. It needs clearance behind the cutting edge, just as a turning or parting tool needs clearance to cut properly, and that is what you do when you grind the drill. It is like creating a fine feed corkscrew.
The chisel point is just that, a rotary chisel, it is an inefficient cutter of metal.
No hand ground drill will be perfect, it just can't be done, but you can get it near enough so that :-
It cuts easily (get the clearance right).
It cuts size (get both cutting edges the same angle and length).
Get the above right and the chisel point angle, looking at the end of the drill, will be correct.
Teenut posted a very good description on the rec.crafts.metalworking newsgroup years ago that some people swear by. It might be worth looking it up, it is a good tribute to remember Robert Bairstow.
I have old hands now but they can still remember the swing action that gets even a 1/16" drill ground right, even if I have to use a loupe to see the end properly!
IanR
mklotz
Well-Known Member
I have his description filed away.
If anyone wants a copy of it, email me and I'll send it along.
If anyone wants a copy of it, email me and I'll send it along.
Hi Bogs and Sid,
The price could well explain why I have not got one and you can indeed buy oodles of decent drills for that money.
On the voltage front, I already have a 240-110 transformer, but even with US prices you have to add shipping and then add VAT all of which could have bought quite a few drills.
For our across pond cousins, we do use 110V over here for "site" power tools through transformers but the frequency is 50Hz.
Note to self, must finish making the Potts kit.
Ned
The price could well explain why I have not got one and you can indeed buy oodles of decent drills for that money.
On the voltage front, I already have a 240-110 transformer, but even with US prices you have to add shipping and then add VAT all of which could have bought quite a few drills.
For our across pond cousins, we do use 110V over here for "site" power tools through transformers but the frequency is 50Hz.
Note to self, must finish making the Potts kit.
Ned
