Taper Turning set-up

Any Mathmaticians out there? Have built the Hemingway Taper Turning Kit for my S7 and want to turn an ER collet taper, half angle 8 degrees. In the instructions using an imperial barrel mike to set the tool it gives a formula of Arctan(.025"/5.000" which then says that equals 0.2864789 degrees. Now I'm a very long way out of School but I make that degree value Arctan( 0.0225"/5.0". My calculator for those numbers shows a value of 0.31824 degrees if I'm it doing correctly. Then mike setting should be 8 deg/0.31824 not 8deg/0.28648. Can anyone confirm or point to what I might be doing wrong please?

Hello Graham,

I got numbers that didn't agree with yours, maybe because I believe the FULL taper angle is 8 degrees, but in practical terms, if you have an ER collet to test your taper against, I would set the attachment up for a trial cut and test with the collet, using indicating blue as you go. Take light cuts, making adjustments, it is quite surprising what a difference a 2 thou shaving makes, and continue until you get the correct fit. I would be inclined to practice on scrap first until you get it right

I am handicapped really since I don't know what the finished tool should look like, nor how you set it up.

Regards

Brian

Graham

When as suggested by Brian testing the collet fit in the bored taper make sure you have a max size ground rod in the collet, saves it collapsing at either end to match an incorrect taper.

Emgee

8 degree is the ER half taper. I know because I made an 8 degree square (actually a 82 degree one) so I can set over my topslide for making hem without any faff.

Neil

Not totally familiar with the tool but from the figure you are using I would assume the pivot is 5" from the micrometer adjuster.

If so you need to offset by 0.703" or if it works like a 5" sin bar 0.696"

Edited By JasonB on 26/10/2015 20:23:06

Working it out a bit more it seemsd the micrometer moves on a 5" arc.

so 2x5 x3.142 = 31.420" circumferance

31.42 / 360 = 0.087" = 1degree

0.025/0.087" = 0.287degree per 0.025"n the micrometer dial which agrees with whats in the instructions

So to get 8deg thats 8/.287 x 0.025 = 0.696" which means it works like a 5" sine bar so easiest thing to do is use an online sine bar calculator to get whatever angle you want. like this one

I use my DRO readings to set up tapers. But that depends on the toys your DRO has.

Thanks for everyone's input. Did try to make the taper using the top slide and then using blue on the collet itself with a dowel in it to adjust TS but just couldn't get the top slide adjusted correctly which is why I went to the taper turning tool. Jason's calc (many thanks for that Jason, it is a 5" arc) gives the same figure as in Hemingway's instructions so will try that out and see what the result is but couldn't match their figure using the Arctan function on the calculator which puzzled me, must be doing something wrong but can't twig what.

Hi Graham

You have to be carefull with the trig functions on calculators because the default is radians not degrees.

HTH

Cheers Michael

Just finished turning the taper using Jason's figures, well pleased, blued it in to check and looks good. Thanks again to all who responded. GW

When I make the internal taper for ER collets, (So far have made at least seven) I do it the quick and nasty way by setting over the Topslide by 8 degrees (maybe my Far Eastern graduations are better than we think). Then, horror of horrors, I wrap a strip of fine emery around a collet and polish with the (collet+emery) in the new taper.

DON'T press too hard or the tapers will grab!

So far am unaware of having had any problems with collets not holding drills, end mills, taps, or work.

It may be a bit crude but seems to work.

Howard

Without knowing the exact geometry involved the differences appear to arise depending on whether the 5" distance is the hypotenuse or the adjacent side of the triangle on which the calculations are based.

I'll take my nerd hat off now.

Neil

Howard Lewis:

You have reminded me that I drew attention to an effective and accurate way of setting the topslide in an earlier thread. See:

http://www.model-engineer.co.uk/forums/postings.asp?th=85534

If the aim is to get as close to 8 deg as we can with our equipment, then the conventional graduated scale on a topslide, regardless of its origin, is not the most certain way to achieve it, as I sense you would agree.