Is my lathe level good now? Precision Matthews PM1236T

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TonyBen

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I'm gearing up to do some chamber cutting and barrel threading. My lathe was set up good enough to do what I've been doing the last 18 months, but I was not confident that it was good enough for precision cutting threads and chambers using the tailstock.

I bought one of those EDGE products alignment bars, a new Bison MT5 dead center and a brand new Starrett 12" level. I don't have any 123 blocks, so I used the flat in front of the carriage to level the bed. I'm solid from end to end. I already had a Skoda MT3 live center for my tailstock and I bought it new, so I know it hasn't been abused.
I seated both centers with a block of wood and a rubber mallet. I also checked both centers and both had nearly no measurable runout. My B&S indicator needle drifted maybe 0.00005" while rotating.

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Headstock to tailstock level...

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I used the EDGE alignment bar and got the tailstock aligned from side to side down to 0.0001" but decided to check the height of the centers as well. Before alignment, I had a bout 0.003" difference between the headstock and tailstock. The tailstock was higher than the headstock. After leveling, the tailstock was now 0.001" higher than the headstock.
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I also used the alignment bar to level the bed from end to end.
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I have a backplate and a dogleg, so I'll do a final cut later but I've never used them before. it wasn't until I tried to get set up to do a test cut that I found out the dogleg was't long enough to reach my backplate. I'll rig up something today to drive the leg.
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I also need to find a way to lock down my cross-slide since the DRO encoder covers up the locking screw.

Tony.
 
I would still do a two collar test to verify. I trust it more than anything. After using the Starrett 98 that would of been my next step.
 
Collar test? You mean turning a piece of steel or aluminum at both ends to verify the sizes are the same?

I made some posts for my backplate this morning. I just need to get some bolts to secure them in place.

Tony.
 
Thats right. It needs to be large enough diameter to be self supporting since you wont be using the tailstock.
 
You can also do the same between centers to verify tailstock to headstock alignment. The Edge test bar is good for that but only over its short distance.
 
You. are. fine.
Barrel threads aren't that critical (donning Nomex underwear, as we used to say...). Chambering is. You didn't mention what chambering technique you'll use, but at this point I'd say your lathe is dialed in and the biggest impact will be how you set up the barrel.

GsT
 
A Starrett #98 level is not accurate (sensitive) enough to level a lathe or other machinery that is subject to twisting or sagging, that is the province of the #198, it is 10 times as sensitive as the #98, or .0005" per graduation. The #98 is more of a millwright's tool, suitable for rather rough leveling; I have both, and use the #98 for rough leveling and the #198 for final leveling, the bubble can look perfect with a #98 and be a mile off with the #198. Having said that, a lathe does not need to be level, it just needs to be aligned, except for lathes with three pairs of legs, where the bed could be level at both ends, but can sag or be twisted in the middle, there, leveling is pretty much necessary to remove sag or twist. In the end, the two collar test is perhaps the best test for proper alignment.
 
GeneT45 said:
You. are. fine.
Barrel threads aren't that critical (donning Nomex underwear, as we used to say...). Chambering is. You didn't mention what chambering technique you'll use, but at this point I'd say your lathe is dialed in and the biggest impact will be how you set up the barrel.

GsT
Click to expand...
Completely agree. I like to cut the barrel threads to fit into the receiver with just a little drag to assure concentricity. Cut and try, repeat until happy. Not very scientific but it seems to be a reliable method. Theoretically the taper of the threads should make the barrel self aligning but a little extra help doesn’t hurt.
 
For now, I'm chambering using a Bald Eagle floating reamer holder. I would like to upgrade to a JGS tailstock floating reamer holder instead, but that's another $275 or so...

For alignment though the spindle, I have an indicator rod, a range rod, dial indicators (one with a standard tip and one with an extended tip) and pilot bushings. The reamer is a JGS 3-flute carbide roughing reamer. I'm set up to cut 30 cal and 6.5 at the moment.
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In the past, I have just used the indicator rod in both sides of the headstock with a 4-jaw chuck and a spider. I adjusted until I got as close to zero as I could, then used the floating reamer holder to chamber the barrel. I had trouble though with my last one as I was using a finish reamer and the barrel was short chambered using a core drill and not a roughing reamer. I couldn't actually hold the reamer when it would catch and I eventually had to shut off the lathe and turn the reamer by hand, using the tailstock to apply pressure.

That's what made me want to upgrade to the JGS tailstock reamer holder.

Tony.
 
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