That .013" cut seems like quite a lot to me, I may be wrong but I always believed that when doing this type of check the smallest depth cut is used to minimise any tool spring, work spring etc. which will affect the results, I would have thought that a few tenths of a thou per cut would be used.
Unwanted Taper ?
- Thread starter Danuzzo
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That .013" cut seems like quite a lot to me, I may be wrong but I always believed that when doing this type of check the smallest depth cut is used to minimise any tool spring, work spring etc. which will affect the results, I would have thought that a few tenths of a thou per cut would be used.
fcheslop
Well-Known Member
More chance of the tool just rubbing and not cutting .
goldstar31
Well-Known Member
This conflicts with the views of non other than Leonard Sparey in his book the Amateurs Lathe. Sparey designed many of the engine designs which are still followed today. Martin Cleeve( Kenneth C Hart) author of Screwcutting in the Lathe and also the designer of the Swing Tool and many articles in Model Engineer and other mags wrote about taking virtually imperceptible cuts in steel. In other. In other words, creating steel wool so fine that it would crumbled as dust between the fingers- and merely dirty them.
Suffice to say that I have suggested the existence of such gems seemingly without anyone noticing.
Again, screeds have been written about stting a lathe tool to the correct cutting height to cut correctly.
John Moran as GadgetBuider.com writes freely on his 7 X14 lathe etc. Again, it is excellent-- and free of copyright
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fcheslop
Well-Known Member
We live and learn
I will stick by my original comment
cheers
I will stick by my original comment
cheers
goldstar31
Well-Known Member
Greetings Frazer
From Sparey's book, he was using a knife tool--
At centre height
with an approach 'cut' or rub at less than 3 degrees.
In other words, not much different to your comment.
However, with sufficient power- and that excludes low powered Myford and certainly these 7x14 variety, you can literally push metal off. Negative carbides and brute force on rigid machines!
Digressing a touch, even the recommended positive carbides with chip breakers are relatively blunt compared with those sharpened with progressive grades of diamond dust/paste
Clearly, YOU know all this but I'm adding this for others who cannot distinguish between the need of metal removal and only precise metal removal for 'measurement'
As you know, and I know, there is one helluva problem using a light lathe where really removal to prese limits should be carried out by grinding. another interesting ball game, eh?
Meantime, best wishes
Norman
Goldstar31 and fcheslop our ideas seem to differ and that's fine we have all had different experiences and are all entitled to our own opinions.
I guess I must work differently to you, and you are probably better machinists than me, I don't think I could have made a decent job of my my Quorn grinder build if I wasn't able to take small depth cuts - I haven't had much success taking the last 10 or 15 thou in one cut and getting it bang on, I usually take deeper cuts until the last 3 or 4 thou and then go a thou or so at a time, I get a feel for the amount of tool and work spring at this stage and feed in accordingly, sometimes I'll take the last 2 or 3 passes without increasing the depth of cut, each pass takes 0.5 thou or so and I can usually get to my target diameter + or - 1/2 thou.
I guess I must work differently to you, and you are probably better machinists than me, I don't think I could have made a decent job of my my Quorn grinder build if I wasn't able to take small depth cuts - I haven't had much success taking the last 10 or 15 thou in one cut and getting it bang on, I usually take deeper cuts until the last 3 or 4 thou and then go a thou or so at a time, I get a feel for the amount of tool and work spring at this stage and feed in accordingly, sometimes I'll take the last 2 or 3 passes without increasing the depth of cut, each pass takes 0.5 thou or so and I can usually get to my target diameter + or - 1/2 thou.
The lighter the cut on my taper issue, the greater the taper issue. Don't know what it means. Just my personal observation. Even after the shim, it went back to a taper on the aluminum. By the way, I took a Bridge City straight edge to the bed length wise, and I found a small gap between the ends. This was with the shim. I didn't measure without the shim. Don't know the significance of this; but, I did not think it was a good thing.
fcheslop
Well-Known Member
Retailer, I dont doubt that youre machine will do as you say and often do the same myself
As to better machinists Im only a toy maker and have illusions on that matter
The thing I doubt is that you can dial in 0.0001 cut on a machine like this and it will give a constant cut and I wonder why the machines owner is so concerned about 0.0001 ..
If in the past I wanted to work to that level it would have gone on to a grinder either cylindrical or otherwise .
Keep well and safe
kind regards
frazer
As to better machinists Im only a toy maker and have illusions on that matter
The thing I doubt is that you can dial in 0.0001 cut on a machine like this and it will give a constant cut and I wonder why the machines owner is so concerned about 0.0001 ..
If in the past I wanted to work to that level it would have gone on to a grinder either cylindrical or otherwise .
Keep well and safe
kind regards
frazer
I think you are misunderstanding me - when I say a thou I am referring to 1/1000 of an inch or 0.001 inches this is one division on the cross slide so it is do able, I see you are thinking 0.0001 which is a tenth of a thou and you are right I know I couldn't dial in 0.0001.
goldstar31
Well-Known Member
Retailer
Building a Quorn involves a lot of boring. I followed Chaddock and George Thomas by making two 'between centre boring bars. In pother words for the two 1" bed bars have to be a tight fit for 3 holes, dead parallel and +0.003" for the split one. Then being a cast iron casting, one has to ensure that once cutting the casting, it doesn't spring shut. Thomas found out( and so did I). He found it on the Mark1 castings on the the Versatile Dividing Head whilst I found it on making the original Westbury mill drill. But this is light years from someone who is writing here for assistance- and seemingly not taking a blind bit of notice.
Chaddock refers to a half thous cut on the grinder as a whopping cut.
ALL my tool and cutter grinders apart from the Clarkson have mere 1/6th HP 2880 rpm motors
Danuuzzo
Might I suggest that you seek professional advice- anf have your - new?- lathe returned to what is was on leaving the factory
Building a Quorn involves a lot of boring. I followed Chaddock and George Thomas by making two 'between centre boring bars. In pother words for the two 1" bed bars have to be a tight fit for 3 holes, dead parallel and +0.003" for the split one. Then being a cast iron casting, one has to ensure that once cutting the casting, it doesn't spring shut. Thomas found out( and so did I). He found it on the Mark1 castings on the the Versatile Dividing Head whilst I found it on making the original Westbury mill drill. But this is light years from someone who is writing here for assistance- and seemingly not taking a blind bit of notice.
Chaddock refers to a half thous cut on the grinder as a whopping cut.
ALL my tool and cutter grinders apart from the Clarkson have mere 1/6th HP 2880 rpm motors
Danuuzzo
Might I suggest that you seek professional advice- anf have your - new?- lathe returned to what is was on leaving the factory
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Danuzzo: just thinking are you having issues with aluminium ? I noticed in an earlier post you mentioned turning a piece of steel with acceptable results, aluminium can be strange stuff and is known to 'gall' easily I always give aluminium a good squirt with WD40 when machining.
Just trying to glean anything useful that I can learn from this. But in doing so, I reckon that maybe you have a wrong starting point? A regular 3-jaw chuck is - at least when I was taught in the 60s - a "jobbing" centre: I.E. Ok to grip something approaching round while you machine the part "to drawing". But as it is made from a series of components - aligned with sliding clearances - it can never be "truly accurate". To work with something "true", you need a collet chuck, high precision chuck or mandrel, work between centres, etc. And any machined length needs to be supported, as during the cut the side pressure from the tool will cause distortion in the part that you can measure with high precision measuring tools. Incidentally, how you hold the micrometer and operate it, can (WILL) give you variation. Measure a single diameter 30 times and then do the stats to see how accurate (Repeatable) you are? Put the mic on the bench, rub your hands together and clap once before each measurement. Have you run a clock (DTI) along the length of the machined bar? (stationary of course), after a "finish" cut? - Incidentally, for lathe work I never expect to work to within 0.001" That needs a precision grinder... Do you control all the temperatures to 20 degrees C. for machining and measuring? When auditing Car component suppliers, we would sack them if they didn't control everything when measuring. Plus or minus 2 degrees C. in the calibration lab was DISASTER!
I should have mentioned I usually set the compound rest over to 30deg, so If I need to advance the cutting tool 0.0005" (1/2 thou) for a fine cut I advance the compound rest 0.001", this moves the cutting tool just under 0.0009" towards the head stock and also 0.0005" (1/2 thou) in towards the work piece, this is nothing new and I don't doubt that it is used by some forum members.
goldstar31
Well-Known Member
I'll check again-- Sorry
Yes, G H Thomas could remove a 1/5th of a thous with a top slide advance of 4 thous
Yes, G H Thomas could remove a 1/5th of a thous with a top slide advance of 4 thous
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Unless you spend major money on a lathe or mill and have a very good maintenance schedule (not just giving it a clean and a squirt of oil) I dought you will achieve the accuaracy you are chasing, in fact I would be suprised if the average machine could achieve that given the variables in manufacture. Far better is to get to know your machine recognise its limitation and work around them, if it is still a problem then do as someeone has allready suggested get a grinder, and deep pockets.
OK, I'll bite.
Why are you trying to achieve such high levels of accuracy and precision?
What are you actually trying to make on the machine? I'm struggling to think of a reason for trying to gain the standards of accuracy and precision that you specify
All the best,
Ian
Why are you trying to achieve such high levels of accuracy and precision?
What are you actually trying to make on the machine? I'm struggling to think of a reason for trying to gain the standards of accuracy and precision that you specify
All the best,
Ian
Those who are asking me (OP) why I am looking for less than .0005" taper in 2" or even 1", I was under the impression, maybe mistaken, that any lathe, without tailstock assistance, should be able to achieve this kind of tolerance. Please educate me if my expectations are too high.
