Threading issue.

B

bigngreen

Guest
I've been struggling to get smaller threads to come out with the finish I would like, looking through a magnifying glass what I'm getting is small tears in the thread and it's a little rough, it's only an issue on smaller fine threads on muzzle brakes. I can open up and true the threads in an action or thread a barrel for the receiver and they come out very smooth and good fitting but when I go down it craps out on me and in cleaning them up I end up a little under size from where I want to be. I'm running HS inserts and Viper Venom oil, speeds from 45 rpm to 250 rpm, barrel is through the head stock, tried feeding straight in and at 29.5 with the compound.
 
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Try running your cutting edge just a little higher??? Like raise it ten thou or so? IMO this gives you a relief more akin to that generated by a conventionally ground bit with a relief rake. It doesn't generate any rake but the relief may help......

al
 
bigngreen said:
I've been struggling to get smaller threads to come out with the finish I would like, looking through a magnifying glass what I'm getting is small tears in the thread and it's a little rough, it's only an issue on smaller fine threads on muzzle brakes. I can open up and true the threads in an action or thread a barrel for the receiver and they come out very smooth and good fitting but when I go down it craps out on me and in cleaning them up I end up a little under size from where I want to be. I'm running HS inserts and Viper Venom oil, speeds from 45 rpm to 250 rpm, barrel is through the head stock, tried feeding straight in and at 29.5 with the compound.
Click to expand...

What trouble you are experiencing can be caused by the tool either 1) dull edges-for small threads must be very sharp, 2) not enough top or side clearance on the tool, 3) tool is above or below center-slightly above is OK but too much will tear threads. 4) taking too large DOC (depth of cut) especially on the last few passes (remember if you are infeeding with your compound it is direct reading so it feeds twice as much as your cross slide....there are a few other issues but I am just starting my cirst cup of coffee.
 
I've been setting the tool up on center best as I can, it has a fresh HS steel insert and all seems to be very sharp and correct. I'm feeding about .005 to start then backing of to .002. The issue is more pronounced with factory CM barrels, I've braked a few Brux SS barrels and they are much nicer threads.

I've been centering the tool by lightly pinching a thin machinist ruler against the work, is that adequate for getting the tool height correct or is there a better tool?
 
I grind my own HSS tools. Very sharp with lots of clearance. I set my compound at 29.5 degrees and feed with it 2 thou per pass, then down to 1 thou per pass and then 1/2 thou per pass. Usually 45 to 60 RPM, I go for a good fit rather than a fast time. I try the fit with that particular brake when it gets close. When it threads on most of the way snugly I lightly touch the top of the threads with a fine file and then spinning in reverse using a piece of 220 grit paper bent over on itself drag that in the thread grooves a few times. Then check the fit again. I want it to fully thread by hand. I will thread another 1/2 thou until it does, always ending up with the reverse polishing. It seems to work for me.

I set the tool point very slightly below center. I use a leveling tool made for this - I bought it from Brownell's many years ago. Machine set up gauge, page 455, catalog 64.
 
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Remember, the smaller the diameter, the less surface feet per minute. I have always found that the best results in threading are at the highest RPM that your equipment, and you, can tolerate..........jackie
 
bigngreen said:
I've been setting the tool up on center best as I can, it has a fresh HS steel insert and all seems to be very sharp and correct. I'm feeding about .005 to start then backing of to .002. The issue is more pronounced with factory CM barrels, I've braked a few Brux SS barrels and they are much nicer threads.

I've been centering the tool by lightly pinching a thin machinist ruler against the work, is that adequate for getting the tool height correct or is there a better tool?
Click to expand...
If you are threading finer than about 24 TPI you are feeding too much per pass for sure, especially when nearing full depth. Many CM barrels, especially hammer forged ones are not super machinable.
 
Ok...... regarding "above" and level and "below" center. When you said "HS inserts and Vipers Venom" I made a logical jump (perhaps wrongly) that you were using flat-topped replaceable inserts made of HSS. The type of inserts you "sharpen" or knock the bue off by rubbing them on a flat stone.

Remember that neither the tool nor the workpiece knows from "center" all the two know is the angle generated between the surfaces. A flat topped tool bit needs to be set above center to achieve the same clearance angle as a well raked bit set well below center.

al
 
I had a similar issue while cutting 32TPI threads. Dad had me set my tool a little bit higher than dead center and i went up 25RPM and all was fine. Thats what i did anyway. Lee
 
Thanks for the help, it's looking like I'm of center, slow and aggressive! Dennis, thanks for the leveling tool advice, found it and I'm thinking that will help. I have a take off Rem barrel of the same size so I'll whittle it down to a tooth pick. I'm capable of cutting at a higher speed but I chicken out when doing something I don't want to screw the pooch on.
 
bigngreen said:
Thanks for the help, it's looking like I'm of center, slow and aggressive! Dennis, thanks for the leveling tool advice, found it and I'm thinking that will help. I have a take off Rem barrel of the same size so I'll whittle it down to a tooth pick. I'm capable of cutting at a higher speed but I chicken out when doing something I don't want to screw the pooch on.
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Find out exactly what your lathe centerline dimension is....( manual or measurement) make a block that sits on lathe carriage that height.Set tool height with indicator and block as gauge.On small stuff .150" and less...set tool .005" below center.
No guess work.
bill larson
 
bill larson said:
Find out exactly what your lathe centerline dimension is....( bill larson
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One way to do this is to chuck up a piece of metal, brass is good. Take a facing cut all the way to the center of this piece. Then set up your threading tool by looking across the point of the tool and the center of the just machined piece. The closer to the just machined piece and the tip of the tool are together the more accurate this exercise will be.
 
JerrySharrett said:
One way to do this is to chuck up a piece of metal, brass is good. Take a facing cut all the way to the center of this piece. Then set up your threading tool by looking across the point of the tool and the center of the just machined piece. The closer to the just machined piece and the tip of the tool are together the more accurate this exercise will be.
Click to expand...

That is how I do it most of the time.
 
alinwa said:
Ok...... regarding "above" and level and "below" center. When you said "HS inserts and Vipers Venom" I made a logical jump (perhaps wrongly) that you were using flat-topped replaceable inserts made of HSS. The type of inserts you "sharpen" or knock the bue off by rubbing them on a flat stone.

Remember that neither the tool nor the workpiece knows from "center" all the two know is the angle generated between the surfaces. A flat topped tool bit needs to be set above center to achieve the same clearance angle as a well raked bit set well below center.

al
Click to expand...

I've been mulling over the insert and the kit comes with two inserts and I've been rocking it how they came and I've been using the insert that is has 0 degree but the other one has 11 degrees to it, maybe I need to maybe swap and try it out. I think I should be able to narrow it down now, more than likely I need to tune my set up a little, speed up the lathe speed and slow myself down, I maybe getting a little cocky with it and I need to take it easy!!
 
bigngreen said:
one has 11 degrees to it, maybe I need to maybe swap and try it out. I think I should be able to narrow it down now, more than likely I need to tune my set up a little, speed up the lathe speed and slow myself down, I maybe getting a little cocky with it and I need to take it easy!!
Click to expand...

The insert with the 11 degree top clearance will make a BIG difference in less machinable materials like CM.

Cocky is OK, just make sure you wear good eye protection and keep fingers and clothes away from the moving parts.
 
One way to get "on center" is to measure from the 12 0'clock position of your part down to the tip of your cutter. When this measurement = radius, you are on center. I use the "depth rod" on my calipers.

Wayne
 
Dennis Sorensen said:
I grind my own HSS tools. Very sharp with lots of clearance. I set my compound at 29.5 degrees and feed with it 2 thou per pass, then down to 1 thou per pass and then 1/2 thou per pass. Usually 45 to 60 RPM, I go for a good fit rather than a fast time. I try the fit with that particular brake when it gets close. When it threads on most of the way snugly I lightly touch the top of the threads with a fine file and then spinning in reverse using a piece of 220 grit paper bent over on itself drag that in the thread grooves a few times. Then check the fit again. I want it to fully thread by hand. I will thread another 1/2 thou until it does, always ending up with the reverse polishing. It seems to work for me.

I set the tool point very slightly below center. I use a leveling tool made for this - I bought it from Brownell's many years ago. Machine set up gauge, page 455, catalog 64.
Click to expand...

Dennis, can you explain the method you use with the tool you cited?
Thanks!
 
Superman said:
Dennis, can you explain the method you use with the tool you cited?
Thanks!
Click to expand...

The tool has a level on it and a ledge under the level you contact the tool point with... Opposite the level is a V groove you place against the round stock you are going to machine. When the V groove is held against the round stock and the point of the tool is under the level and the bubble indicates it is level, the tool is centered on the round stock.

It takes longer to explain it than it takes to do it...
 
Another one-of-a-kind tool from Brownells is the TDC punch with the level machined in. Absolutely invaluable for timing barrels.....
 
Often we read posts and have an idea that just ain't worth bringing up for the sake of more conversation if oyu know what I mean. Regardless, sometimes its a hellofa lot easier to patch the problem than to repair the cause. Often I take my chuck out of gear and turn it by hand for the final pass or two. If your lathe allows, pop it out of gear so the motor cannot drive the chuck yet the rest of the gears still function and turn the chuck by hand. Let me know if it improves any.

Cheers
 
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