setting 8 degree taper for ER collet holder

I am in the process of making an ER40 collet holder and have just finished the end that threads onto the lathe mandrel. Now comes the tricky bit of machining the 8 degree taper on the collet end of the holder.

Is there a way of accurately setting the topslide to this angle or is it best to set it as close as possible and then check with a collet and then nudge the topslide and take another cut until a good fit is obtained.

Doug

End of the day it has to fit the collet you have so making it to fit seems the best to me .

When you offer the collet up with blue on it to check for contact make sure you have a piece of bar or a broken cutter shank in the collet to stop it closing up and just following what you have machined.

John S.

The way I did it was to set the 8 degree nominal using the topslide scale; hold a bit of silver steel in my 3-jaw and slide on an ER collet of the same nominal size as the steel, which meant that it slightly gripped the steel and hence ran true; and tweaked the topslide for no error on a DTI run along the side of the collet. Had to be careful that the DTI plunger avoided one of the slots. Seemed to work fine.

I do it similer to John. Best to put a bit of bar in the 3 jaw and turn to size, then it will be concentric. I made a DTI holder from a bit of 1/2" sq. bar, put in the toolpost and drill from the chuck, then it's on center hight. Mine is 8mm dia, saw a slit and drill a clamp bolt hole to gently clamp the spindle. Set the top slide to zero run-out. Still have to check with blue but usually spot on.

Take your time and use a Dial Indicator to set up a taper on a hobby lathe (trigonometry)

Thanks for the replies, the tip about placing a bar in the collet when testing the fit is one I will follow.

Doug

If you have accurately ground surfaces on your topslide and cross slide, like my mini-lathe, once you have the accurate angle make a little square that you can use to reset the topslide in future. Mine has come in handy for collets, another holder and the odd job needing a taper of 'about' 8 degrees.

Neil

If the aim is 8 deg, as opposed to matching an existing taper, then P J Smith's Taper Turning Gauge is well worth considering. It works on the sine bar principle, is straightforward to make and has the great practical advantage of positively aligning the topslide before it is tightened. Unfortunately, the web page describing his device seems now to be "unavailable" but I have the relevant files on disk and no doubt there is some way they could be posted to this site together with a photo of my own version if these are of interest.

The gauge works equally well for larger and smaller angles so would come in for morse tapers and 40 deg included angle collets as well as the ER variety. Finally, it provides an opportunity to brush up one's trig!

I note from one of the helpful threads here on ER collets that John Stevenson found it necessary to correct the nose of his collet holder by grinding it in situ and would be interested to know if he has written up the process anywhere. I imagine that most of those who make their own holders turn the taper but, of course, the commercial item is ground (and, presumably, hardened).

But not that hard, I managed to turn the socket of my nose fitting ER25 holder to correct an eccentricity. I just used a new small radius TC tip in a boring bar.

cheers,

Rod

Little secret, wrap a piece of very fine wet and dry or emery (ideally a tired bit that has been used) around a collet, making sure there is no overlap but most of the collet is covered. Oil the abrasive, then gently push into the bore when the mill is running. This is not to make the chuck mrore accurate, just to give the bore a final polish.

Neil

Hi ega, I would be very interested in the details of the taper turning gauge you mentioned. If it is possible could you upload details of the construction to this site.

Doug

Some further interesting postings.

Douglas Johnston: so far as I can see I can only upload JPGs to an album. For the moment, therefore, I have uploaded only the JPGs in Smith's description. Beyond these, as well as explanatory text, there are a number of GIFs; I will give some thought as to how to make these available and also photograph my own version and post in due course.

Thanks to John and Ega for the information provided. My collet chuck body has been sitting in my workshop for a while now while I have been doing other things, but I must bite the bullet and have a go at machining the taper.

Doug

I have now posted photos of the components of my gauge and of its use for setting the Myford topslide.

By way of additional explanation, "R" on the gauge label is the distance between centres of the two 12mm dia columns; these project below the base plate sufficiently to engage the c 8mm dia rod when it is located in the dovetail of the topslide (it is, of course, necessary to remove the top of the slide to make the setting).

"N" is the wall thickness of the setting ring derived by trig as indicated on the label.

The gauge is held on the topslide base by the clamp on the other side from the rod. Removing and replacing the top of the slide is made easier if one has dowelled the gib as recommended by GHT. I believe that late model Myfords have a flat-topped slide and it may then be possible to operate the gauge from the flat top provided that the geometry is correct; it is necessary to align the gauge with the slide travel.

In the photo the setting is being made to a test bar held in the tailstock. The bar could perhaps better be placed in the spindle taper. For convenience, Peter Smith's original suggestion was to align the gauge to the extended tailstock barrel but on the Myford this would mean a limited "R" distance. The 8 deg setting ring is shown supported by friction only but in practice it may be more convenient to provide packing so that it sits at the appropriate height and to verify the setting position by trapping slips of cigarette paper between gauge and test bar.

I hope this is clear and that it helps someone other than me - if so, give thanks to Peter Smith.

Here is a good method for setting your topslide to a precise angle using a DTI and the sine of the angle to work out the travel required.

I have just made one of these for my own jig borer and this idea worked a treat.

**LINK**

Phil

ega,

Thanks for posting the additional photos

... all is very clear, now.

MichaelG.

.

Phil,

Many thanks for posting that link

Anything about BCA is welcome !!

MichaelG.

Hi Doug

Another possible method of measuring the top slide angle accurately is to take a cut off a piece of scrap bar in the chuck with the top slide at a position near its extended position and repeat the cut with the top slide near the other end.

You need to know the exact distance the top slide has moved (with the dial & leadscrew) and you need to measure the two diameters of the turned bar. The rest is down to a calculator.

I put some small marks on my top slide and tend to re-use the stepped bars until they disappear.

The method is theoretically spot-on, providing the lathe is accurate to start with

Peter

Have now made at least nine holders for ER collets, from ER20 to ER32, for various purposes.

The last one, also involved making three collets to hold 1, 2 and 3MT shanks, and even with only one set of slits, in unhardened steel, all seems to function as required)

I just set the Topslide over to 8 degrees, using a magnifier to watch the graduations.

After carefully boring the taper, (I gauged how far to go by measuring protrusion of a collet from a commercial holder, and maching until I got JUST a little over) Final op is, as Stub mandrel says, Wrap oiled fine emery around a collet and use to hone/polish the bore. Don't push too hard or it be snatched out of your hand!

All my holders seem to work quite satisfactorily, so the technique can't be too far away.

Howard