Dialing in the tailstock with a Coaxial indicator

JonathanK

JonathanK

New member
I am using a coaxial indicator to dial in my tailstock...I first dialed the coaxial indicator in the 4 jaw chuck then inserted the indicator point in to the inside of the MT quill of the tailstock. I have the side to side spot on but I have .0025 spread up and down if Im reading the indicator properly. It says each mark is .0005 off axis and it moves 5 marks when reading it up and down. This makes me think its .0125 high or low, this isnt a whole lot but Im not sure its acceptable in the kind of work Im trying to do.
 
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Sounds like it is .0025" off. If you indicator reads in 1/2 thousandths and it moves 5 marks, that is 2.5 thousandths or .0025". If it is only .00025" in actuality, you're good to go. Two tenths (.0002) is a really small amount and not anything for you to be concerned with. If it's .002 you MIGHT can get it a little better.
 
Jonathan, most likely your tailstock is a touch on the high side. They typically come that way new so that over time you have room for them to wear. You need to determine if it's low or high. Being a touch high, as yours appears to be isn't a bad thing, especially considering it's such a small margin.
 
JonathanK said:
Yes it is high
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Mine is 0.005" high on one lathe, 0.003" high on the other. For everything associated with chambering and fitting barrels, and in fact anything I can think of associated with gunsmithing, through the headstock or in the steady rest, it doesn't matter as long as one uses a floating reamer holder that has radial compliance.

Fitch
 
.0025" is normal for a tail stock or cross slide. They build them that way from the factory. I'm assuming your using a Blake or one of the clones, and you should be aware that they do have problems with built in lag when your trying to split that last half thousandth of an inch. I always finish out with an Interrapid or Best Test
gary
 
I understand that some tailstocks on the new import lathes come in a little high with the thought that they will wear in over time....whatever, it's fine with me. But, let your lathe run for 15 or 20 minutes and warm up. Then re-check your tailstock.
 
eddief said:
I understand that some tailstocks on the new import lathes come in a little high with the thought that they will wear in over time....whatever, it's fine with me. But, let your lathe run for 15 or 20 minutes and warm up. Then re-check your tailstock.
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very true heat affects all machines i've found. our brand new makino cnc machines at work require a 5 min spindle warm up before machining that and gravity with a heavy part can weigh down and take some of that out as well
 
it's pretty much a standard practice to build a lathe with the slides and tail stock a little high. Been that way for as long as I can remember. When I scraped the slides and bed on a lathe I usually shot for about .00075" high; with the tail stock being about .0012" high. I have scraped them in dead on the centerline, but you get to do that one over again in about a year or two.

It is a good idea to warm the bearing packs up on a precision lathe or machine center. Ten minutes at 150 rpm is plenty good enough for a lathe and twenty minutes at 500 rpm is about right for a CNC machine. Most of the better machine centers come with a spindle growth compensation device (if it don't have one don't buy it!), and more than one lathe comes with a simpler version. Still with a lathe it's kind of a moote point if the bearing packs were designed right. All the growth is shifted to the rear of the headstock on purpose, plus they were never designed to be .0005" or less machines (but some will do that). Most engine manufactures build what is known as a "precision lathe" and a "roughing lathe". The differences are in the headstock design and bearing packs. Rarely can you convert a roughing machine over to a precision machine.

I long for a brand new 10" Monarch EE!
gary
 
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