# lathe toolpost grinder



## rcfreak177 (Oct 2, 2010)

Hi, 

  just wondering if anybody out there has made a tool post grinder for grinding crankshafts on a lathe, Probably a silly question because I know for sure it has been done before. I have checked out the web and seen a few types, I have also thought of modifying a 5" angle grinder and mounting either a silica type wheel ( the white one) or a diamond wheel. I don't know how well this will work due to the backlash in the bevel gear setup. Just after some idea's at the moment. Or plans. any help will be greatly appreciated. Below is the machine I will be mounting a grinder to. and also a possible diamond wheel to be used. I am also not sure how the wheel would go grinding hardened and tempered 4140 steel with 0.010" material to be removed

Regards Barry.

https://www.machineryhouse.com.au/Products?stockCode=L682

http://cgi.ebay.com.au/6-X-1-8-PREC...ultDomain_0&hash=item51927c696f#ht_2464wt_802

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## Blogwitch (Oct 2, 2010)

Your machine is basically the same one as I have, and I use a dedicated toolpost grinder, with the correct sized wheels (critical).

When precision grinding on a lathe, it really requires a dedicated grinding spindle, not something cobbled together from some other bit of kit.

There has been at least one good toolpost grinding spindle build on here, so maybe a search will come up with what you really require.

People use all sorts of things to do a bit of grinding, and I am very surprised there have not been more accidents. Maybe there have been, but have not been owned up to.

Grinding is really one thing that shouldn't be played around with unless you know what you are doing. The peripheral speed of grindstones is much higher than almost anything else you will come across in a workshop, and as such, when things do go wrong, the consequences can be a lot more serious and at unthinkable speeds. Even I had a close call the other week on my surface grinder doing a job for a chappie from another site, luckily only nearly requiring a change of underwear and trousers, and I hopefully know what I am doing. It was only because that I had things set up as I did that nothing more serious happened other than a chipped wheel, which has now been classed as unsafe by myself and has been thrown away.

I have shown this before, reasonably cheap toolpost grinders with the correct wheels can be had, as long as they comply with your electrical standards.

http://littlemachineshop.com/products/product_category.php?category=-1731696149

I am not trying to put you off grinding on the lathe, but there is just a little more to it that turning a wheel and grinding a bit off a chunk of metal.

I will be grinding the crank journal on a future build of mine, to obtain the exact finish and dimensions I want, but for sure, it will be done with the correct tooling.


Bogs


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## Tin Falcon (Oct 2, 2010)

Barry :
No silly questions here but we do get some silly replies on occasion. 
Toolpost grinders can be made or purchased. IIRC cost of a new one ranges from about $150.00 US to $1500.00 US. 
IIRC there is at least one build thread for a tool post grinder here. 
grinding a crank on the lathe is done the same way you turn a crank on a lathe. 
It is a simple matter of setting up the crank so the part to be machined runs true on center of the lathe. the ends of the crank are offset. There are probly a hundred public domain books out there that can explain it better than I and there is like a south bend book . I will see what i can dig up for you. 
As far as the diamond wheel NO diamond wheels are for carbide NOT STEEL. A good quality alox wheel will do just fine .
and remember to protect the lathe bed from abrasive dust. 
Tin


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## GWRdriver (Oct 2, 2010)

I echo what Bogs and Tin have said, especially what Tin says about covering the lathe shiney bits, and in fact all nearby precision machinery, to protect them from airborne abrasive dust which will occur no matter how small and quick the job. The other thing is that the grinding of small bits is a delicate process which should only remove a few tenths at a time so in this case 010" is far too much grinding allowance. If there is any way you could reduce the allowance to maybe .001"-.002" the proces will go much better, and quicker.


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## Tin Falcon (Oct 2, 2010)

I agree with GW .010 is too much to leave for grinding I worked in a shop that did grinding IIRC we left .005 or less to grind off. 
Grinding takes time and patience heat is the enemy when working plus or minus a tenth or two. Also flood coolant to keep the dust under control one machine used filter paper to remove the crud from the coolant. 
Tin


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## bp (Oct 2, 2010)

When I worked for a living, we had a tool and cutter section which did not only T & C grinding but also surface and cylindrical grinding on products. It was tucked away in a corner of the machine shop. I would have preferred it to be in its own room, but politically it had to be "within the four walls" of the main machine shop. It had a dedicated dust extraction and filtration system, to go along with its dedicated air con, we had to spend A LOT of money to try and ensure that no grinding dust escaped into the main shop.
Fortunately their was a management change which allowed the T & C section to be put in its own room....we built an airtight partition.
Keeping grinding dust away from other machinery is very very important.
cheers
Bill Pudney


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## rcfreak177 (Oct 3, 2010)

HI,

  Thanks for the support. I have operated cylindrical and centreless grinders previously and am well aware of the safety aspect. Mind you a reminder of the potential hazards involved are most welcome. The fact that I have never attempted tool post grinding in a lathe before especially with an offset swinging nature is why I am asking you guys for advice. The last thing I want is to have an accident at home especially when it could be witnessed by my wife and young children. Unfortunately the grinders that Little Machine Shop sell will not quite accommodate the offset that I need. I think I will attempt to make my own unit to spin a 6" dia wheel *(Not a diamond wheel, Cheers Tin)* and will ensure the balance of all rotating parts is up to scratch and also the wheel itself.

*Thanks Bogs,* I have followed quite a few of the threads created by yourself and have learnt quite a lot. I am only a young bloke with approx 10 years machining experience but have found myself learning rapidly every day. This model engineering is quite different to machining on larger machines, Although the principles are much the same the outcome can be quite different. I took your advice recently on the 9x20 lathe saga and purchased a larger machine to make my still small but larger parts
(I hope that makes sense), Most of my paid lathe work has been done on machines from 3 meter to 8 meters between centers. Cheers Mate, I am looking forward to the future thread you speak about to do with crank grinding.

*All Members with this experience* please advise me with personal thoughts on this topic

Kind Regards Barry


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## Dunc (Oct 3, 2010)

Pop Mechanics, http://books.google.com/books?id=RdMDAAAAMBAJ
and 
Pop Science, http://books.google.com/books?id=iigDAAAAMBAJ&source=gbs_summary_r&cad=0_0#all_issues_anchor
offer plans and how to info.

PM: plans Aug 1944; how-to Feb 44 & Nov 49

PS Aug 41
As well the Nov 62 issue had a plan to adapt a Dremel as a tp grinder.

Model Craftsman, Jun 1937, available from 
http://www.dm.net/~lughaid/grinder.zip
offers another plan.

Search the article indexes of HSM, etc 
http://www.homeshopmachinist.net/articleindex


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## Blogwitch (Oct 3, 2010)

Barry,

I think John Stevenson made one out of a small offhand grinder that mounted onto his cross slide.

I think that would be about the only 'safe' way to mount such a large wheel on the sorts of machines we use. The large spread of the bearings can support the weight and size of the wheel required. If you look at an offhand, it is the wheel on the RHS that you would use.

I am sure John posted a picture of it somewhere, and if he reads this, maybe he can post it again.


Bogs


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## sharlotendo (Dec 1, 2012)

One of the main tricks, is to make sure the grinding wheel is dressed with a diamond. Depending on the speed the diamond is drawn across the grinding wheel determines the micro finish on the finished work. Micro inch finishes are done with a scratch pad. After a facing cut is done on the workpeice,a light one! you can measure the workpiece diameter...then take the wheel off the workpeice and with a pencil mark the work with the pencil while its spinning..then bring the wheel back onto the workpeice untill it cleans off the pencil mark...Now you can take the job down to size from there.After getting the coolant on the job.


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## MuellerNick (Dec 1, 2012)

> I am also not sure how the wheel would go grinding hardened and tempered 4140 steel with 0.010" material to be removed



You'll discover, that with just 0.25 mm allowance, you can throw away your crank. Even without grinding.
After hardening and tempering, it will be bent more than just the 0.25 mm.
On straight shafts in the 300 mm range, I leave an allowance of 1 mm. And after hardening, that often enough is a close call.


Nick


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## sharlotendo (Dec 1, 2012)

When you dress the wheel,if you drag the diamond across it fast, it leaves it rough..this is used to remove a lot of metal.Before the final finish you can redress the wheel slowly to get the micro finishes.There was always a bit of rivallry between the "precision grinders" and the "Turners" Using a roughened wheel you take lots of metal off fast, then go down to the tenths of thous on a redressed wheel for finishing...the turners would get it down to half a thou. and finish it off with emery cloth.
  For Crankshaft regrinding, there was always about ten thou. of hardened steel to play with,as long as it had a couple of thou of the hardner left it would clean up.This was on the Universal grinding machines, they could remove metal as fast as a lathe tool.


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## petertha (Dec 1, 2012)

Blogwitch said:


> I have shown this before, reasonably cheap toolpost grinders with the correct wheels can be had
> http://littlemachineshop.com/products/product_category.php?category=-1731696149
> Bogs


 
Hi Bogs. Are you using that particular grinder yourself or seen it in action first hand? Reason: I still daydreamin about building a little tool & cutter grinder & it occurred to me maybe buying it purely to strip the motor & drive assembly might be worth it $150 even if the spindle etc was junk. It looks similar to these (gulp) $4000 lathe toolpost grinders. Makes me think they might be cutting a few corners  

http://www.artcotools.com/dumore-series-25-tool-post-grinders/

But I've seen some horrible stories about offshore bench grinders so I'm a bit reluctant, purely from a safety point. Seems like with the big namebrand toolpost grinders the 'quality' is maybe morese in the spindle assembly & bearings etc. Thats the grey area for me, if I could make that myself well enough, the motor & belts & fixtures might not be that bad. Sorry for the sidebar conversation, I'm interested in this too!


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## goldstar31 (Dec 2, 2012)

You might think about using a wood router.

Years ago, and I think that this is what is being recalled, I bought a Bosch POF 45 or 50( I forget) which but it started its days as a tool post grinder.
Stripped of the wood cutting bit, it revealed a 43 mm collar.

Perhaps John S will confirm but his double ended grinder thing was a mock up of cheap Chinese 6" DE, a three way vice also Chinese and a set of collets which would make up a tool and cutter grinder.

Around the same time, the late Derek Brooks( ?Brookes) wrote up an article in Model Engineers Workshop( issues 16 and 17?) of a similar rig but using a wood router.  Later, I am guessing that the Raymac also had a router as its motive power.

OK, having babbled on, the Quorn body makes an excellent tool post grinder. 

For those who want something 'simpler', the late Ian Bradley described one in his 'The Grinding Machine' I believe in the MAP series.


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## MuellerNick (Dec 2, 2012)

A router is running too fast to be usefull for grinding crankshafts in the lathe. He needs something like a bench grinder with a grinding wheel.
Depending on the stroke of the crank, those wheels can get quite big!


Nick


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## goldstar31 (Dec 2, 2012)

MuellerNick said:


> A router is running too fast to be usefull for grinding crankshafts in the lathe. He needs something like a bench grinder with a grinding wheel.
> Depending on the stroke of the crank, those wheels can get quite big!
> 
> 
> Nick


 
OK,in practice  the Quorn spindle will accept 5" wheels. It simply needs a revised pulley system. I made up a Quorn years ago and before getting the Clarkson it was quite suitable. One worker ( Phillip Amos) moved his Quorn  to various tasks including on his milling machine.
The book by Dennis Chaddock is still available and the castings probably in the UK and certainly in the US.

Going off at a tangent( only a slight one) there is quite a lot on the net about humble 'Tinker' by Norman Tinker and the plans etc are available from Guy Lautard. Basically, its power comes from a cheap 6" grinder.

I've my old plans from Norman and seriously wondered whether to make it up to do wood shredder cutting drum which are quite sizeable


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