Plastic shim

[Peter G. ShawParticipant @peterg-shaw75338]

As part of my slow, oh so slow, improvement to my Warco MiniMill, I am now at the stage where I need to adjust the Y axis to correct the front/rear tilt as it seems to be a bit out.

Reading other forums, it seems that one possible source of problems is the head itself which is in two parts and that other people have successfully corrected the tilt by inserting appropriately sized shim between the two parts in an appropriate place to force the two parts to adopt slightly different positions. It seems "Rollies Dad's" method is the way to go.

Anyway, some years ago I bought a set of plastic shim material from RS Components which I have mainly used as final stage packing for lathe tools. My question is about what will happen to this stuff if placed under a sufficiently high pressure: will it creep and thus destroy the adjustment?

Ideas? Thoughts?

I could, of course, buy a steel shim assortment, but if the plastic stuff is going to be satisfactory, and I already have it, then why waste money on stuff I don't need?

MTIA,

Peter G. Shaw

[Peter G. ShawParticipant @peterg-shaw75338]

[David JuppParticipant @davidjupp51506]

Yes – it is likely to suffer from creep, though it depends to some extent which plastic. Higher melting point plastic will suffer less. Thermoset maybe won't creep.

Plastic have lower modulus than metals, and lower yield stress – so you will be able to 'squeeze' plastic rather more than with metal to 'adjust'.

[Peter G. ShawParticipant @peterg-shaw75338]

David,

I've had a look on both the pack, and the website – only described as "plastic".

The website states "Plastic shim performs the same function as metal shim, but has additional uses as a seal and as a barrier to prevent corrosion between dissimilar materials".

Although RS say that it is their own make, the PAR group describes "Plastic" shim thus:

Material Specification 'A

These specifications applies to thickness from .001” to .015” as detailed and are produced colour coded from polyester films ('Melinex', 'Mylar', 'Hostaphan&#39 to meet the particular demands of the engineering, automotive, electrical and electronic industries. Polyester materials are remarkably tough with very high compressive and dielectric strengths, very low water absorption, and excellent dimensional stability over a wide range of temperatures and good resistance to most chemicals, ozone, direct sunlight etc.

So I rather suspect the RS stuff may be Polyester

Does that modify your thoughts?

MTIA,

Peter G. Shaw

[Neil WyattModerator @neilwyatt]

Fit a DTI in the spindle and do some checks to make sure it's not simply column tilt.

The minimill is essentially the same design as the X2 (as far as I can tell) and all the error in my machine was in the column, I was also able to greatly increase the size of the column bracket contact patch, helping rigidity.

There's an absolutely brilliant article on the subject in MEW issues 199 & 201 – quite life-changing in its breadth and scope – though modesty makes me refrain from naming the author.

Neil

[David JuppParticipant @davidjupp51506]

Well – it's better than some plastics.

Given that you have the shims – why not try them out anyway? Take a note of whatever thickness you end up using – then monitor it. If it isn't stable, you'll know what thickness steel shim to acquire.

[Peter G. ShawParticipant @peterg-shaw75338]

Neil,

I intend to do that, but the first thing is to check the alignment of the head with the column using Rollies Dad's method – a description by rudydubya re Mini-Mill Spindle-Column alignment applies. It's on the Homemodelengineering website.

I've got yours printed out ready.

David,

Yes of course I can try them out, it was just the long term I was thinking about. And, just to be completely honest, I never thought about doing it, and then changing to metal later. Remiss of me, I know, but then that's me all over – I often need a dig, or a kick, or something, before I see the blindingly obvious. Thanks.

Peter G. Shaw

ps. To Neil. Sorry about the slight mistake about 10 mins ago. I didn't see the adjustment until it was too late. You'll know what I mean. Just use the second one.

[Brian WoodParticipant @brianwood45127]

Hello Peter,

I've used that plastic shimming to true up the very slight droop on my Dore Westbury mill column where the socket/clamp fits the base casting; it needed 0-005 inches if I remember. I really don't think you can generate enough clamping pressure over the faces to get the shimming to creep; that might however be a problem with joint faces at elevated temperatures.

A second use at my last place of work, this time 0.018 inches thick to slip into the joint gap on the split line on the tailstock on a big DSG lathe to compensate for severe weat on the front end of the bed shoe. It made a big difference to the exit diameter of large holes drilled from the tailstock.

I endorse it. Apart from everything else it is so easy to use and shape with scissors.

Regards

Brian

[Russell EberhardtParticipant @russelleberhardt48058]

I made shims out of kitchen aluminium foil to true up the column of my mill about 10 years ago and it's still spot on.

Russell.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Peter, I have used this **LINK** in industry for shimming gearboxes, electric motors, pumps and many other such things for many a year, and have not had any problems with creep ect. and many spare parts are often accompanied with a selection of ready made shims of the very same type of plastic. If what you have is the same, it should be OK to use.

Regards Nick.

Edited By Nicholas Farr on 15/06/2015 19:41:27

[Peter G. ShawParticipant @peterg-shaw75338]

Brian,

Thanks for that.

Russell,

Now why didn't I think of that? After all, I have the book by L.C. Mason about building a small lathe in which he advocates using aluminium foil to create sliding gaps. (Hope that makes sense – it's not particularly good grammar.)

Nick,

That's the stuff I have, but in the 6" wide version.

So, all-in-all then, it's a goer (ooh, slang, not good!). And all I need to do is to find the time, after fence building, cutting the grass, making some tidgy pins for the caravan, going on holiday, visiting the medics for follow-ups, and so on, and so on,… and so on….. Oh dear, I really don't know how I'm going fit it all in.

Thanks one and all,

Peter G. Shaw

[Author]

Posts