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ER Collet Sizes

Another nice way of setting up precise boring angles is to use the fact that, on many lathes, the lefthand machined edge of the topslide is accurately parallel to the topslide dovetail axis. This is easily checked with a tenths clock bearing against this surface while the topslide is moved over its full traverse. This will not only check the parallelism but also check that the gibs are properly snugged and do not wobble as the handle is turned.

With known parallelism the required angle can then be setup by a 5" sine bar and gauge block spacers resting against the side of the topslide.

A jury rigged clamp may be used to hold the sine bar in position but I find it more convenient to provide artificial sideways "gravity" by a couple of supermagnets rescued from a junk computer hard drive and temporarily stuck to the topslide side with spacers and double sided sticky tape. The mild steel spacers are chosen to set the working airgap to no more than

1/8".

With the sine bar safely anchored, the topslide will then be correctly set when the sine bar surface is parallel to the spindle axis. This is checked with a clock, located on the bed, and bearing on the the sine bar surface. It should show no movement as the lathe carriage is traversed to move the clock tip along the whole length of the sine bar.

Jim

Reply to
pentagrid
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That should be right in most cases. But don't forget that -per definition- if you face work, the resulting "plane" has to be concave or plane.*) But in most cases it will be concave. So the angle will be a tad off.

*) 0.03mm over 300mm according to one standard.

Nick

Reply to
Nick Mueller

That only applies to cross slide generated surfaces. It does not affect this method because only the topslide moves. The residual 0 to slight concavity of a cross slide generated plane surface has no effect because the cross slide is stationary. The cross slide should of course be locked near its working position while the topslide is being clocked into its correct angular direction.

What does matter is whether the bed axis (i.e. saddle traverse direction) is truly parallel to the spindle axis. However any significant error here is immediately obvious because such a lathe would be unable to turn a true cylinder - all workpieces would come out slightly tapered.

Jim

Reply to
pentagrid

Yes, but it also is a result of the alignment of the cross slide to the axis. It is not dead-exactly 90°

But you took the cross slide as reference. Or did I get that wrong?

BTW: If been thinking about that problem a few days and really like the idea with the sine bar!

Nick

Reply to
Nick Mueller

Reread the original post carefully, The cross slide is locked and not used as a reference. The setup sequence will still give the correct answer even if the cross slide axis is many degrees in error.

Jim

Reply to
pentagrid

Thanks, I did that. And got it now. Your sentence ...

| .. is to use the fact that, on many lathes, the lefthand machined edge | of the topslide is accurately parallel to the topslide dovetail axis.

... led me to the conclusion that you actually meant the cross slide. Because I have problems finding the *left* edge that is parallel to its dovetail on a top slide. Well, it can be rotated, but in normal position I only have back and front.

Nick

Reply to
Nick Mueller

I have a set of 8 imperial marked ER40 collets (1/8, 1/4, 5/16 etc). They are genuine imperial sizes, not remarked metrics, as I've checked them against various metric ones and there are noticeable differences. So I guess they do exist - can't imagine the Yanks putting up with metrics for example.

-Neil F.

Reply to
neil f

Interesting Neil, I have heard of these but never seen them. J&L list them but when I have bought them they were still marked as metric. Ironically at the time the 'imperial' ones were cheaper.

-- Regards,

John Stevenson Nottingham, England.

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Reply to
John Stevenson

The imperial set of ER16 collets that come with the Taig mills ARE imperial as well. Only 4 mid range one's though, so you still need to find small and large ones.

Reply to
Lester Caine

I just bought an ER32 collet chuck 125mm dia and Myford backplate to suit from ARC. I tried it in the three possible fitting positions possible , and got 0.03,0.04and 0.05 mm runout. As the runout got worse two of my mounting bolts got slightly harder to tighten. The

0.03mm runout is fine for my purposes (I was quite pleased with this actually!), but I guess if I needed it better I'd start by making the backplate mounting holes a tad bigger.

Stu G

Reply to
stooby-doo

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