Back plate dimensions and tolerance

[Neil AParticipant @neila]

Hi Bernard,

With your dimensions and Jason's photo I now understand what it is your are trying to produce.

I had not realised that the larger Warco and Amadeal lathes had that type of spindle nose configuration. I did not realise that the chucks were not direct fitting but needed a separate backplate. I was thinking of the smaller lathes style. I was completely wrong!

I think that Jason's advice of machining to a "feel' fit is good, although as you say pulling everything apart to check the fit is tedious. Do you have another backplate to machine a plug gauge for checking purposes?

Neil

Edited By Neil A on 05/05/2023 19:57:21

[Neil LickfoldParticipant @neillickfold44316]

Our lathe came with a snug fitting nose on the backplate, but the chuck was not running true , no matter what key was used to tighten down on test pieces, from, 8,10,12,16,19,25mm samples. So I skimmed the chuck register on the backplate itself, so the flange face had now swash run out, and then took 0.1 off the register. Remounted the chuck, with the screws lightly nipped, and put in the 12mm pin, indicated it to zero near the chuck and looked at it from 30mm out. It was fine. Snugged the screws, and checked all the other common sizes that I use and it was really good, within 0.02mm over the range with 12mm being my zero. I don't do cuts heavy enough to be moving the chuck, and anything with interrupting cuts I use the 4 jaw chuck.

To assemble very tight fitting parts, a very light smear of castor oil , will make the parts easily assemble. The down side is that castor oil can turn to a gum and then make the parts hard to dis assemble. There are some other oils and greases that allow tight parts to easily assemble. One that surprised me is the lube grease for DMG Moori machines grade 000 grease. Really expensive in NZ, but is around 30 pound for a 1 litre bottle that will last a lifetime.

I can not underestimate the cleanliness required when changing chucks or face plates on machines . The screws needs to be really clean and free of any dust, grit etc. So a little time to make sure everything is very clean, really pays off in the long term.

Jason has nailed how to make a test plug for making a new backplate to fit your lathe. To try and get the very close finish, if the compound slide is set at a very shallow angle like 0.5 deg, you can use the movement on the compound slide to make the very small diameter changes. There is no issue with polishing to final size, once you get down to the last thou or 0.02mm on diameter as you sneak to the final size. The register is better to be slightly in the tighter side rather than the looser size. My chucks and backplates came with a relief on the first 3 4to 4 mm of the length of the spigot, so about 1/3 is relieved slightly.

Neil

[bernard towersParticipant @bernardtowers37738]

If you set your compound slide to approx 5.75 degs it will give you a tenth cut for every div.

Edited By bernard towers on 05/05/2023 21:19:59

[duncan webster 1Participant @duncanwebster1]

This is one instance where a micrometer would be better than a digital caliper. I'd make a dummy to as near as I could manage to the register as I find measuring holes accurately a lot more difficult than spigots.

[DC31kParticipant @dc31k]

Posted by Bernard Start on 05/05/2023 19:11:07:

I find it extremely funny (and anoying) that this basic dimension is not in the manual.

I think you said in an earlier post that you had a Myford. Are you aware of any factory/manufacturer-produced drawing for the Myford lathe that shows this information? Sure, everybody knows what a Myford spindle nose looks like, but these are third party drawings not factory ones.

If you picked a random sample of lathe manufacturers*, how many of them would provide the drawing? For a standardised spindle (e.g L-taper or D1 camlock), the best you will get is a reference to the appropriate international standard, which you could then purchase from the standards body.

* my list, based on available online manuals: Schaublin, Colchester, Harrison, Monarch, Holbrook, Hardinge.

[Bernard StartParticipant @bernardstart12493]

I wish I had a go – nogo plug gauge or I'll be happy with the dimensions.

[CirclipParticipant @circlip]

i find it extremely funny trying to machine some thing to the 'Perfect' state when once the machine has been 'In use', limits and fits and tolerance goes out the window and wear takes over. Careful measurement of the spindle nose gives exact diameter and clamping screw pitch/diameters are sloppy anyway.

Regards Ian.

PS. Don't forget to allow for temperature compensation.

[DalboyParticipant @dalboy]

My first one I made from Ali and I am remaking it is steel as well as making it a little thicker.

On my WM280v there is a mark which is there so that the three jaw chuck is fitted in the same orientation each time so on the backplate I did the same which brings it very close to the same settings. The PCD on this is as Jason's 75mm.

I turned the face which attaches to the spindle first and then attached it to the lathe before turning the outer face which attaches to the ER collet chuck(like you this is ER32).

In this last photo I have rough turned the blank ready to do the same turning as I did for the Ali one. I am a total novice and I am sure that if I can do it then you should be able to do the same. I know there will be some that say I did it wrong but I got the first one working just fine and it ran concentric when fitted each time (yes I did measure it)

[Bernard StartParticipant @bernardstart12493]

Thank you Circlip, This machine is just off the production line and has not been used in anger to wear it.

[Bernard StartParticipant @bernardstart12493]

Thank you Dalboy, I see from your classic work bench you have lots of experience!

I see you measured it. What was the register measure (5x.xxmm)?

[DalboyParticipant @dalboy]

Posted by Bernard Start on 06/05/2023 11:43:38:

Thank you Dalboy, I see from your classic work bench you have lots of experience!

I see you measured it. What was the register measure (5x.xxmm)?

The workbench is scarred from many years of woodworking must replace the top as it is ply.

I took my measurements from the lathe register and also the chuck sizes if you do that then you should get it correct size

[Bernard StartParticipant @bernardstart12493]

Thanks Dalboy, I am belt & braces and my skill with gessing sticks in restricted space and internal diameters is poor.

I like to get measure three times, one independant before cutting.

There seems to be a reluctance to discuss and share actual dimensions. Do you know why?

[DalboyParticipant @dalboy]

Posted by Bernard Start on 06/05/2023 13:39:30:

Thanks Dalboy, I am belt & braces and my skill with gessing sticks in restricted space and internal diameters is poor.

I like to get measure three times, one independant before cutting.

There seems to be a reluctance to discuss and share actual dimensions. Do you know why?

If there are any discrepancies in measurement from lathe to lathe then using someone else's measurement may lead to an incorrectly fitting part that is why it is best to take them directly from the machine in question.

Hope that explains it

[Bernard StartParticipant @bernardstart12493]

Not at all Dalboy. Sharing throws more light on the subject.

However, I have just managed to stretch a Mitutoyo 25-50mm to 52.04mm

[DMBParticipant @dmb]

Years ago, I bought a brand new S -7 and 3 jaw chuck. I struggled to screw the chuck on for the first 2/ 3 ? years when it gradually got easier. I think my experience bears out what circlip said above about tolerances easing with use, when a minute amount of wear takes place. I now use lubricant on the threads to reduce further wear and to make it easier to remove chucks. Never use gummy jollop like 3 in 1. I use that purely for oily surfacing rust free steel stock.

John

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