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Thread: Taper Comparitor !
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2nd May 2020, 02:39 AM #1
Taper Comparator !
Hi Guys,
A couple of weeks ago I posted in the Metalwork General Forum, a thread entitled "Measure a Taper" !
I would like to thank all those that read that thread and those that replied for their notes and offers of help.
I've since done quite a bit of research on line about this subject and come to the conclusion that the ability to actually measure a taper is not as useful as being able to compare an unknown taper to a known one. I found a reference to a simple device for measuring a taper by a guy called "John Aspenleiter" from around 1900. I've also found descriptions of instruments very similar to it but using a micrometer for measuring tapers. So I decided to make my own copy of this device based on Aspenleiter's design.
Warning there are a lot of pictures in this post !
I had a 6 inch length of 1/4" inch thick brass plate that I had salvaged from the scrap yard quite some time ago. So I decided to use it to make the parts that I needed to produce this measuring device. Note that I've called it a comparator rather than a measuring instrument, since I've not taken any particular pains to ensure accuracy. In fact the only carefully made part was the dovetail slide since any play or looseness here would have a large effect.
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I cut a nominal 50 mm wide strip off the brass plate and then cut a 30 mm wide strip. Then I cut a further two 10 mm wide strips. These pieces gave me the base and slide plus the two sides for the dovetail guides. I used a 45 degree chamfering cutter to machine the angled sides for the slide and the guide plates.
I then drilled the guides for M4 fastening screws on the mill using the handle calibrations to get them both the same. Actually looking back, I could have clamped both pieces together and drilled both at the same time and then machined the dovetail angle. In practice I drilled both pieces of guide with a 3.2 mm tapping size drill and spotted through to the base plate by holding both pieces against a straight edge.
Using the slide I then spotted through the guide at the other side holding them tightly together with a pair of spring clamps. This ensured that the dovetail slide and the guides were parallel to each other. In practice I had to force them apart and take the sharp edges off the slide with a file before the slide would move easily.
Its difficult to see in the pictures but I did relieve the base between the guides by 1/2 a mm. I also polished the edges of the slide and guides with a scotch brite pad and a spot of oil which made a huge difference to the ability of the slide to move smoothly without being tight.
22-04-2020-002.jpg 22-04-2020-003.jpg
The method of comparing a taper relies upon four equal diameter pins that are set a short distance apart in two pairs. One pair being fixed to the slide and the other being pivoted and able to move such that any tapered object placed between them would displace the movable pair.
To this end one pair of pins is pressed into one of a pair of brass pieces so that they are perfectly vertical with respect to the dovetail slide surface. The other brass piece after having the pins pressed into it has a pointer attached. The moving brass piece and pointer are pivoted on a hardened steel pin pressed into the base of the dovetail body.
22-04-2020-011.JPG 22-04-2020-010.jpg 29-04-2020-004.jpg
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The steel pins are 4 mm diameter pieces of silver steel rod (Drill Rod) pressed into 3.9 mm drilled holes approximately 40 mm apart. Not having a press, I used a short length of 12 mm diameter bar drilled so that the 4 mm silver steel rod slid inside with about 12 mm protruding. This was placed in the chuck of the drill press and then the quill was used to press the rod into the holes in the brass strip.
Doing it this way ensures that the measuring pins are vertical with respect to the brass strip and in turn vertical with respect to the dovetail slide.
The movable pair of pins has a simple aluminium pointer attached to the brass strip by two brass M4 dome headed screws. The screw heads were milled down so that approximately 1 mm above the screwdriver slot remained. The idea here was that the screw heads would lift the aluminium pointer off the top of the dovetail slide base.
Originally I was going to use a small ball race for the pivot, but found that it allowed the pointer to droop and also the pins were no longer vertical, so a hardened steel pin was used instead. This actually proved much better than using a ball bearing, even a so called precision one.
29-04-2020-002.jpg 29-04-2020-001.jpg
These two pictures show the completed device. I used a couple of turned bits of aluminium rod to act as spacers on the pins of the slide and to level up the hight between the base of the pins.
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This picture shows what happens when the tapered item drops into the gap left between them.
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1/2" round bar. MT3 socket.
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MT2 mandrel. MT2 Taper reamer.
I cut a bit of Ikea tape measure up to get the calibrated strip under the pointer. The little black dot on the paper tape is the zero point originally derived from a 25 mm parallel placed between the measurement pins.
It is quite accurate as a comparator and should be able to be calibrated in inches per foot or whatever scale you would want to use. As I said earlier, I didn't take any particular care in construction to ensure accuracy but if you want or need to compare two or more samples of a taper then its fine.
Thanks for looking. All comments welcome.Best Regards:
Baron J.
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2nd May 2020, 01:37 PM #2Most Valued Member
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Thanks for the pics and posting how it was done, BJ. An interesting piece of kit.
Just putting it out there, if the pointer was 12" long from the centre of the pivot, and was set to 0 on the tape, would it not then read as Taper per Foot?
KrynTo grow old is mandatory, growing up is optional.
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2nd May 2020, 05:29 PM #3Senior Member
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Just to add a little to John's excellent post (which I hope he doesn't mind) on making the taper measuring device, attached are some photos of one made in Worchester USA and its based on the same principal, in actual use its quite hard to get a good reading due to the shortness of the taper face and it has to be on axis, that's where John's handiwork would be much easier to use. Well done. Alan.
bar.jpg bar1.jpg
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2nd May 2020, 06:42 PM #4Diamond Member
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A very useful device BaronJ. I just found this Taper Calculator whilst doing a google search to see what is around https://www.newmantools.com/tech/tapercalc.htm you just input the data and it does it for you.
All The Best steran50 Stewart
The shortest way to do many things is to do only one thing at once.
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2nd May 2020, 07:07 PM #5Most Valued Member
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Hope you don't mind Stewart, but I posted this https://www.newmantools.com/tech/tapercalc.htm into the Conversions and Calculations at the bottom of the Forum page.
KrynTo grow old is mandatory, growing up is optional.
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2nd May 2020, 07:30 PM #6Diamond Member
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I don't mind at all Kryn, a good idea actually as more people will see it. There looked to be Apps available as well on different websites.
All The Best steran50 Stewart
The shortest way to do many things is to do only one thing at once.
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2nd May 2020, 07:52 PM #7
Hi Kryn, Guys,
That is very true and a useful idea. Thank you for pointing that out !
I openly admit that I didn't take as much care in making it as I should have. That pointer isn't truly square. It reads a couple of mm more on one side of the zero than the other.Best Regards:
Baron J.
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2nd May 2020, 10:27 PM #8Most Valued Member
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I find it amazing that someone else can see something in a product and suggest improvements on it
Didn't notice the angle not being correct.
Stewart, an app is no good to me, I can't even get chromecast to work!!!!!!!!
KrynTo grow old is mandatory, growing up is optional.
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4th May 2020, 02:16 AM #9Senior Member
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Nice tool. Did John Aspenleiter have some kind of tool for the inside taper?
Pete
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4th May 2020, 11:18 AM #10Golden Member
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Variation in tapers
Hey BaronJ,
Nice, well done and thanks for the posts.
Am curious - what sort of variation do you see on your gauge when you compare an MT2 to an MT3 ?
MT taper table from this link
Taper Large End Small End Length Taper/
FootTaper/
InchAngle From Center #0 0.3561 0.2520 2.00 .6246 .0521 1.4908 #1 0.4750 0.3690 2.13 .5986 .0499 1.4287 #2 0.7000 0.5720 2.56 .5994 .0500 1.4307 #3 0.9380 0.7780 3.19 .6024 .0502 1.4377 #4 1.2310 1.0200 4.06 .6233 .0519 1.4876 #4-1/2 1.5000 1.2660 4.50 .6240 .0520 1.4894 #5 1.7480 1.4750 5.19 .6315 .0526 1.5073 #6 2.4940 2.1160 7.25 .6257 .0521 1.4933 #7 3.2700 2.7500 10.00 .6240 .0520 1.4894
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4th May 2020, 08:08 PM #11
Hi Pete,
Good question ! I don't know. I did do various searches and discovered that he was an immigrant but that is about all. There seems to have been a lot of unrelated Aspenleiter's around in various countries. I'm not sure exactly how he got credited with the design or idea either.Best Regards:
Baron J.
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4th May 2020, 08:22 PM #12
Hi Bill,
Thanks for your post.
Actually barely any discernible difference. The differences are so small that I can see why a micrometer was used on the commercial gauges. Kryn got it right when he suggested a foot long pointer !
I doubt that I will do anything more with this device. Whilst it works well, it needs far more precision than it currently has in order to use it as a measuring instrument. I suppose that if I'm honest with myself, it was more an intellectual exercise.Best Regards:
Baron J.
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