Taper Turning Question

gotchips · May 31, 2007

I have been using a lathe on and off for over 35 years and anytime I needed to cut a taper which was usually less than 2 inches in length and not really critacle I would just use the compound set at the angle I needed and that was that.Well I have a job that requires a 1/4 degree taper for a 6 inch length. Large dia. is 1.533,small dia.1.481.So far I have tried 8 different times to get the taper attachment set just right but am always about 1/4 degree off.Is there an easy way to get the dimensions as stated or is this to close tolerance to perform without grinding?
Thanks for any suggestions.
Dale

Rod Williams · Jun 1, 2007

i have only done this once, i was turning in inches per foot. i measured out three inches on the tapper attatchment, then set a dial indicator on the cross slide to measure amount of travel of the cross slide while running the three inch section i marked on the tapper attatchment. in this way i could devide the inches per foot ( say .6023 ) by 4 ( .6023 divided by 4 equills .150575 ). i would addjust the tapper attatchment till the cross slide moved .1501".
Note: CRS.. may have to devide the .1501 by 2 since you are cutting on one side of material.
sorry if this is confusing but this was the only way i could figure it out by myself, but the dead center i cut for my spindle on my SB9 came out alright.
some one can correct me if i'm wrong and pint out a simpler way.

Larry Condon · Jun 1, 2007

The purchase of a Mini-Sine Bar will allow you to mount the 2" sine bar the the material being machined and set the taper attachment to the correct angle.

-TJ · Jun 1, 2007

I've worked with the taper attachment of my 10L a handful of times and at risk of blasphemy, I've never found the graduations on the TA to be dead accurate. I've only needed a specific angle a couple times and I've always spent way too long making cuts, adjusting the TA, repeat. Creep up on it in other words.

Without firing up AutoCAD and answering my own question - Is that 1/4° angle the included angle? If your lathe is as worn as mine, that's a tall order given all the slop in the leadscrew etc.

You might have better luck setting the tailstock over 0.026" and doing it that way.

gotchips · Jun 1, 2007

Well,the 1/4 degree is per side,and I assume that when you set the angle on the TA it is also per side(1/2 degree included).The job I have was for only 3 pieces and I have spent way more time on this than it is worth.But at this point I am going to play with the TA and see what kind of tolerances I can come up with.It works great for making a tapered handle or something that who cares if your off a 1/2 degree but for holding a .052 plus or minus .005 taper in a 6 inch length I am going to turn the job down.
Thanks for the suggestions guys.
Dale

-TJ · Jun 1, 2007

Dale - I was refreshing my memory on a taper attachment related item just 2 days ago and I remember reading in the How To Run a Lathe booklet that the taper attachment graduations are included angle. So, to get 1/4° per side, you'll have to set it to 1/2°.

I can check it again, but I'm pretty sure that was for 9, 10K, and 10L+ machines.

Jamie · Jun 2, 2007

Dale;

Those index marks on the taper attachment, are far
from accurate, use an indicator. Use the marks
only to get you in the ballpark, then use the
indicator for fine tuneing. Make a dry run to
measure how much the tool post moves over the
required distance. If not correct, then loosen
the 2 bolts slightly and tap in the required
direction then carefully tighten the bolts.
Make another dry run to check. If still incorrect
repeat the procedure again.

Jamie

gotchips · Jun 2, 2007

You guys are very accurate in your descriptions and suggestions,just like I never use the graduatios on the head of a bridgeport when setting to zero,I always indicate it in.I am going to set the TA so that I get .052 movement in 6 inches and hope that it moves the cross slide an equal amount.

Thanks for the help guys
Dale

Toms Wheels · Jun 2, 2007

The scale on the T/A is approximate. Forget the sine bar on an SB there nothing flat and handy to use it against. Set the T/A about where it should be. You need a carriage stop, or something like it, and a piece of stock of accurate known lenght between 2 and 4 inches long. There is slop in the T/A so start an inch or two before the begining point of cut to take out the slop, try to cut from large to small diameter, so the crosslide is pulling rather than pushing the cutter. lock the crosslide handle. With a piece of say 3" stock held between the carriage stop and carriage move the carriage until the it locks the stock, set a DI against the end of the crosslide, remove the stock, crank the carriage until it hits the carraige stop, read the DI, you want half of the taper in inches,in your case .013" in 3". A small brass hammer is the tool to adjust the taper slide with. You can get it dead nuts, the hammer is the problem, sometimes too much, times too little. Monarch has a knob, to adjust the slide thats a joy.

gotchips · Jun 3, 2007

Gotcha Tom,I did not think of cutting from large dia to small dia,will give it a try this afternoon,Was wondering though if I am getting any slipage on the cross slide from not having the handle that locks the cross slide tight enough.The handle I am talking about is the one that is on top and goes thru the long elongated slot.

Toms Wheels · Jun 3, 2007

The crosslide will not slip, it just adds slop to the system, finish will suffer. Find a nut to use and lock the slide, feed with the compound. In reading you response, you said "I am going to set the TA so that I get .052 movement in 6 inches" you want crosslide travel of .026 not .052 in 6"

gotchips · Jun 3, 2007

Hey Tom,
I got excellant results,right on the money, I was impressed,thanks,yah I tried using the crossfeed handle friday and figured that the compound works a lot easier for turning down dia.I also loosened the locking lever on the TA to go back to the beginning of the cut and then lock it down again to start the cut.
Thanks for the help
Dale

Monafly · Jun 4, 2007

A trick I've used on mine to get the fine adjustment necessary on the TA attachment is to find two points on the TA that I can put a caliper and accurately measure the offset of the top piece. Then when I loosed the bolts and tweak for correct angle, I can tell if I've gone too far or not moved it or if it's move when I tighten things up. If it's a taper I'm likely to use again (MT3 for the tailstock for instance) I record the caliper reading and can then get awfully close on the first try later on.
The graduation marks are just a good guess, as I've never found them to be accurate enough to use without measuring as has been suggested above.

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