Ok I'm not the best at explaining but here goes. Here is the short before the long. For the last 2 years my compound took .045 on the dial at 29.5 degrees to finish to the proper thread depth for an 18tpi 1.062 barrel tenon. The last few barrels my dial has been reading 37. OK now, what I am having happen is about ever .015 or so my threading tool is taking a bigger bite than I am dialing into the compound. I'll feed .002 or .003 on the dial at a time and usually that is what the threading tool will remove. However once or twice through out the tenon the tool gets hungry and takes a bigger bite than I am dialing into the compound. I have looked all the obvious things over and I just can't see what's moving. My lathe is a new import of decent quality with hardly and wear. Actually no wear. I hope this makes since to someone. I need some advise. Thanks fellas. Lee
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threading issue.
- Thread starter skeetlee
- Start date
- Replies 24
- Views 7,458
stonehaven
Hot Rolled
- Joined
- Jan 20, 2013
- Location
- canada
If you are feeding using the compound and take a cut, then pull out at end of thread, restart next cut by zeroing on cross slide. Is your dial on crossfeed moving. I assume you are not using DRO. Put a dial indicator up behind cross slide to verify movements.
JBCGUNS
Aluminum
- Joined
- May 9, 2012
- Location
- Sydney, Australia
I know you said you checked all the obvious things but without knowing exactly what they were - and assuming your tool (insert?) is sharp - have you checked that the centre height of the cutting edge is still where it used to be? If it rides up even a small amount over centre it will start to push and grab as you described.
I will check the tool center this evening. I wouldn't think it would have moved but I guess anything is possible. What I did check was that the compound moves evenly from number to number on the compound dial. I checked with a dial indicator. I do have a dro on this machine. the cross slide seems to repeat zero, confirmed on the dial as well as the dro.
Let me ask this. " please keep in mind I am not a machinist, hobby barrel smith." I have also been noticing when a take a facing cut going into the center, when I back the tool straight back on a piece of round stock the cutter will take a little material on the outside of the work piece, the last .100 or so. the tool doesn't touch the center, just the outside. going straight in and straight back out? does this mean my tool holder has some give and when the tool first touches the work piece its moving?? just thought I would throw that out there?
I have chambered some really good match winning barrels and I do most of my barrel work from a blue print. reason being that most of the barrels I do are for short range, and the actions are glued in. I depend on thread wires. the last barrel I did I had to redo, as the dam threading tool decided it would take a big bite when I only needed a light final pass.
I will check the tool, and report back. I hope its something that simple. I have used this Kennametal tool for at least 50 barrels and it has always worked flawless. Lee
300sniper
Hot Rolled
- Joined
- Nov 14, 2006
- Location
- Greenwood, Ca
What are you using to gauge your finished thread pitch?
thread wires and or a ring gauge. I played around a bit this evening, and my conclusion is that there is some play in the gear box?? A couple weeks ago, the A B C selector on the exterior of the gear box stuck over on c and would not come back to A or B. Dad wiggled around with it and finally got it to move. Now the the dam thing doesn't really feel as if it has the 3 separate positions . the handle will slide half ass all around the ABC range. Basically im not 100 percent sure that even if the arrow is pointing to B that the gear has settled in the b slot perfectly. same with A and C.
I will see about getting into the gear box and have a look this weekend. I just don't see anything else!!! Lee
I will see about getting into the gear box and have a look this weekend. I just don't see anything else!!! Lee
sean9c
Hot Rolled
- Joined
- Oct 5, 2009
- Location
- Anacortes, WA USA
Are you always getting the backlash going the same way?
Oldwrench
Titanium
- Joined
- May 21, 2009
- Location
- Wyoming, USA
This probably isn't it, but as an apprentice I once ran a bunch of threaded parts on a Hardinge HLV that exhibited a variable lead about halfway down. After a lot of head scratching by everybody, somebody noticed the handwheel had a lot of play and when it went over center it fell about half an inch and the slight impact drove the carriage ahead of the lead screw. The owner, who had bought several Hardinges brand new, said he was a frankly surprised that the handwheels weren't counterbalanced. I've since encountered the phenomenon once or twice on other lathes. How I noticed this was, the pitch diameter over wires was small where the thread was wider.
stonehaven
Hot Rolled
- Joined
- Jan 20, 2013
- Location
- canada
When you do your facing, do you lock carriage to bed?
stonehaven
Hot Rolled
- Joined
- Jan 20, 2013
- Location
- canada
better find out why that is happening, not normal for it to pop out. is lead screw bent.
That’s somewhat common, my Monarch does the same thing or at least it did before I balanced the wheel.
It’s good practice to apply a little drag-counter pressure with the carriage hand wheel. Doing so will ensure that the play in the drive train is remove prior to entering the cut and will ensure nothing goes awry during the cut.
A cut that has problems with a skim cut but suddenly takes a heavy cut is a sure sign that your tool is rubbing. Get out your magnifier and have a good look at your tooling.
Good luck, Mike
Son of Sam
Aluminum
- Joined
- Oct 11, 2014
- Location
- South Jersey, USA
Assuming your always moving in the same direction (into the cut) with your compound then I would check for play in the gibbs of the compound. If you can tighten them try moving your tool in or out so that your using a different section on the compound screw and gibbs. FYI- I never cut threads with the compound set to 29.5 like the textbook says. All of my manual machines are set withe the compound parallel to the spindle. I take cuts with the cross slide.
Snug up your gibs, and check your tool geometry and sharpness.
Your threading problem is in too much "freedom" ;-)
The drive gear box (A<B<C etc) has nothing to do with uncontrolled cutting depth.
If you need to, Pull back on the tool post with your free hand. A Dial indicator that shows the actual tool motion is the best diagnostic tool. Worth the effort to make one, I use mag bases.
Your threading problem is in too much "freedom" ;-)
The drive gear box (A<B<C etc) has nothing to do with uncontrolled cutting depth.
If you need to, Pull back on the tool post with your free hand. A Dial indicator that shows the actual tool motion is the best diagnostic tool. Worth the effort to make one, I use mag bases.
Butch Lambert
Titanium
- Joined
- Oct 30, 2002
- Location
- Poetry Texas USA
Kinda like the BR forums isn't it skeetlee?
boucher
Aluminum
- Joined
- Dec 24, 2004
- Location
- Burnet, TX
For threading barrel shanks, I replace the compound with this tooling block.
This is significantly more rigid than the gibs on the compound.
For things that I work with a lot, a few under size ring gauges are easier than thread wires.
This is significantly more rigid than the gibs on the compound.
For things that I work with a lot, a few under size ring gauges are easier than thread wires.
I've had this happen one time or something similar only to realize I didn't lock the toolpost down tight when lining up the threading tool. Actually I guess it was the opposite. I was feeding in and the tool kept spinning away with the tooloost. Wasn't paying attention I guess. Either way I bet its somewhere from the compound up. Like someone else said...grab the toolpost and try to shake it loose. You should be able to feel even a couple thou of play.
How far is your tenon sticking out into space away from the chuck?...assuming you are doing this in the headstock.
How far is your tenon sticking out into space away from the chuck?...assuming you are doing this in the headstock.
300sniper
Hot Rolled
- Joined
- Nov 14, 2006
- Location
- Greenwood, Ca
The OP is now using less movement of the compound, not more than the usual.
If you are actually gauging these with wires, not new/different receivers, then I'm not totally sure what is going on. I'd have to do the math to see what number is closer to correct on an 18tpi thread.
Has anything else changed? Work holding?
If you are actually gauging these with wires, not new/different receivers, then I'm not totally sure what is going on. I'd have to do the math to see what number is closer to correct on an 18tpi thread.
Has anything else changed? Work holding?
I still haven't narrowed it all down yet, reason being lack of time. However I think I feel some play in my crossslide. There seems to be a bit more backlash on the cross side wheel know than when I first got this machine. I am thinking the sudden back motion on the wheel as I back out from the shoulder is the issue? Maybe?? im going to look into this area a bit closer. I may take everything apart and look it over real close.
