Help with taper measurement.

[dwentz]

OK, I am in need of a little help.

I have this Chinese built lathe, its a CZ-300a, but is not like the current CZ-300a's found on the internet. It has a 2 1/4-8 thread on the spindle. The book states that it has a MT 4 1/2 short taper in the spindle. The problem is there is not a standard for a MT 4 1/2 that is a standard. I have found the specs on this taper, and they very from manufacture to manufacture. Some of them say the taper per foot is the same as a MT-6

So I set off to measure it. I put a lever type dial indicator on the cross slide with the ball pointer in the spindle and set it to zero. I moved the carriage 1 inch and got a reading of .029 inches. I was assuming that this would be the taper per inch, but it is not close to any of the standard Morse tapers that I found. Am I missing something?

The goal is to make an adapter for 5C collets and MT3 tooling so I can turn between centers.

Dale

 

[mklotz]

This reference ...

http://www3.telus.net/public/aschoepp/tapers.html

shows the MT4.5 as 0.624 in/ft, slightly less than the MT6 at 0.626 in/ft.

0.624 in/ft is 0.052 in/in but that's the included angle. The half-angle is 0.026 in/in so your 0.029 is close. (Some of the difference may arise from you not having the DTI exactly on the spindle centerline. Not a dig, but measuring a taper this way is an exacting task.)

Given the bastard nature of the MT4.5, I would try measuring the existing taper as accurately as possible and then machining a slug to fit, using Prussian blue to fine tune until you have a good fit.

 

[Maryak]

You should be able to match the taper using the headstock centre as the plug suggested by Marv. That's assuming your Chinese headstock is similar to mine. ???.

Best Regards
Bob

 

[mklotz]

Measuring female tapers accurately is at best a finicky job. For parts I can get on the surface plate, I've used tooling balls and a height gage in the past. (There's a program to do the associated math on my page.)

For lathe HS tapers, I've imagined a process that might work. I've never tried it so I can't validate it but I'll throw it out here for consideration (or rejection).

Machine a thin disk on the end of a short shaft. The (non-critical) diameter of the disk should be a bit larger than the small end of the taper. Make another with a disk a bit smaller than the large end of the taper.

With the shaft mounted in the tailstock chuck, push the disk into the taper until it seats. Accurately measure the depth of the disk below the front of the spindle. Repeat for the other disk. Now you've got two accurate diameters separated by a known distance. A bit of trig and you've got the taper angle.

 

[dwentz]

Thanks for your help.

When I measured it I put the dial indicator on the cross slide, and made sure I was at the bottom of the taper, by taking the lowest reading by moving the cross slide back and forth, before setting the dial to 0. I was approximately square with the spindle, and had the needle as straight as I could get it. I will measure again, and also do the same on my 7x10 that has a MT3 to make sure I can get good numbers there also. I will see if I can square everything up a bit more and get a better reading.

I do not have anything that fits in the spindle. So if I need to turn something between centers I have to put a shop made center in the chuck.

My main problem was that I was not taking into account that the charts were the included angle. Thanks for pointing that out to me.

Dale

 

[mklotz]

There's nothing wrong with putting a (soft) center in the chuck - I do it all the time. Just be sure to take a cut across it to true it before doing anything that requires precision.