having trouble cutting a taper

[ieezitin]

peoples....

I have been trying to cut an internal taper this weekend and have been having a hard time getting it right.

when I slide the male end into the bored hole it seats but if you apply some slight pressure on it you feel a wobble, I applied a little more pressure with an arbor press and it seated well, I then returned to the lathe to bore out a hole, I made one pass checked it and it ran true ( the bored hole that is), I then took it out of the headstock, I detached the stub end from the piece and re seated it, put it back in the head stock and there was miss alignment, it did not seat correctly.

To test my fit I applied chalk to the male end and inserted into the taper hole, gave it a slight twist and then removed it, there was touch marks all over the tapered male stub, it looked pretty fine, I then ran down the tapered hole some fine emery cloth to put a decent finish on it, I did not go hog wild it was more like a buff, I did a chalk test again and got the same reading.

It’s a 2JT male end on a MT2 that I am trying to copy (the 2JT that is). To get my angle I set the piece in between centers and had a .0001 test indicator set in my tool post, I installed a needle point tip to it, I set the elevation to a dead center that I had in the tail stock, I wore x3 mag goggles to see it. I ran the compound slide up and down the male taper and eventually I got it down to 2 tenths of a thou over about 5/8 run, hell if you breathe on the lathe you will get a reading.
My question is, if I am doing anything wrong please let me know and…. How do you all do it?

Thanks in advance Anthony.

[tekfab]

How are you holding it ? between centres ? in a chuck ? in a collet ?

Mike

[Rickabilly]

It does sound like you've done everything right, but...

Center height is super critical and any number of factors will change the height of a tailstock centerheight, from base or way wear, quill wear, damaged taper, damaged center through to a mismatched tailstock, that is a tailstock that has been switched accidentally in the factory or shop (it happens). either measure your centre from a reliable datum for eample the tip of a freshly turned cone in the chuck and then make an accurate guage for repeatability, also the tool tip needs to be on centre as much as the indicator and any clearances in the compound slide will muck you up as when testing with an indicator the slide is unloaded but whe turning with a tool the load on the slide is much higher and therefore clearances can open up.

Chalk is less than an ideal testing medium, it's too thick by a long way also the grain sizes are inconsistent, try engineers /prussian blue, and never fully rotate the tapers relative to each other;
1, coat lightly with testing medium,
2, insert test piece into hole firmly,
3, rotate relative to each other by no more than 1/6th of a turn and maintain side pressure in one direction only,
4, remove and inspect,

Many tapers will work if forced together with an arbor press, so this technique should never be used as any kind of test

And most importantly make sure it is all clean, and I mean super clean when testing tapers.

I hope this helps
Regards
Rick

[Sunset Machine]

A bit confused here too. A slight wobble, yet the chalk test was good. ????? Please detail your method, this is not normal. Look for 50% contact (or better) towards the big end.

"took it out of the headstock." ??? Explain, please. If you're adapting the spindle taper, your chalk-test method comes into question again, this time on the OD of the adapter.

If you're attempting to mount a dead center in the spindle taper, this is all good practice but I use a 3/4" bar with a 60 degree point on it that I true every time. Just grab it with a 3-jaw chuck and re-point it. Lathe dog leans up against one of the jaws. Call me lazy.

[ieezitin]

Mike.

I have a 3MT to 2MT sleeve up my headstock spindle, the 2MT slips into that.

Rick.

Your notes on accuracy are well taken. I thought I had covered everything but when I went back into the shop I noticed my brand new 2MT to 2JT spigot has a TIR reading of .002 run out in the 3MT to 2MT adaptor.
At the moment I have just Locktited my boss to the spigot and I will now never be able to remove it, that’s fine as they are cheep but the moral of the story is check everything. For what I am making I can live with this slight runout.

It’s been awhile since I have given the lathe a alignment check I will do this some time this week.
While we are on this subject has anyone got some good ideas on making a height gage for the tooling setting on the lathe?

Anthony.

[f350ca]

Anthony, I've had the same problem and wonder if the side force is just dislodging the taper. We're dealing with machined not ground surfaces to begin with.
I bored a taper in a coupling to match a tapered end crank shaft on an engine from a gen set. I had the armature to measure the taper, chucked it and set the compound to match the angle as you did. Then made a male taper to check the setting. Used bearing blueing to check the contact, perfect, dry the taper would not slip with minimal axial pressure but as soon as you put side load it would un seat and wable a little bit. Figured it was as close as I could get so machined the female taper with the same compound setting. Got the exact same results with the test rod. Perfect smear on the blueing, would carry torque but side pressure would dislodge it and give a little wable. Assuming the boring bar for the bore and cutter for the male taper were both on center height you can't get much closer than machining the two parts with the same compound angle and I still had the same results as you.
By the way the coupling apparently works fine driving a small hydraulic pump for a wood splitter.

[ieezitin]

Sunset.

The wobble I got is when it first slid into the taper just before applied a slight force to seat it, its hard to explain, it was not as smooth as is should have been, it should have felt like a nice sliding fit, my finish on the bore was quite nice, it’s a piece of stainless. I will later take pictures.

When I honed in on the finish cut I zipped the speed up a bit and worked the minute spring out of the cutter, I was getting dust in the end. Before I did this I worked spring out, I knew I would get a hair more on the zip cut.

But now like I mentioned in my last post i discovered slight play in the adaptor to the 2JT spigot.

Anthony.

[ieezitin]

F350…

You make a good point on the machined finish. My 3MT to2MT adaptor has a machined inside finish, the 2MT x 2JT has a ground finish, saying all that it’s a sleeve I have been using for years, I take good care of my stuff but it wares too.

This is a good case for new people to this hobby that shows how the smallest of little details can make your day go awry… I have been on this now for about 10 hours and its severely punished me.

Same as you……. I have proceeded with the small error and I figure I can live with it, must admit though I want to get it right and I will be overhauling the lathe soon for accuracy, I am glad your project worked out good.

Anthony.

[Rickabilly]

Hello Greg and Anthony,
The strange feel of slight side force dislodging the "fit" is typical of an "Hourglass taper"

The reason that the blued/chalked fit indicates well is from over rotation of the two parts, you see any more than 1/4 turn and the marking can seem like it is all around when in reality the marking is from the wobble of taking a second bite while turning the pieces, so stick to 1/6th of a turn max, the less the better.

So the process is;
1, stick it in with no side force at all till it just touches,
2, turn it in one direction no more than 1/6th of a turn,
3, pull it out and inspect,

Never re check or do a full revolution or apply side pressure.

Regards Rick

Hour glass tapers are equally caused by incorrect tool centre height and worn or badly adjusted compound slide, not locking the saddle slide or compound slide, inconsistent feeding of the compound slide during final cutting of the taper, over extended compound slides and a few other factors.

The reason an hour glass taper causes the funny feel is that at least one point usually the first 1/3rd of the hole the tapers fit well then with just a thou of axial distance outward they "fit" again so a wobble between two good fits.

[f350ca]

Thats the way I check tapers Rick. Just a fine line of blueing then slide the mating parts in on the dry side.
Wouldn't incorrect tool height just give to steep or shallow a taper?