cutting tool radius ??

H

Hal

New member
I have another question on getting a nice finish on ss.

I'm using a Diamond shaped (VCMW 221, 1/64 radius) tin coated carbide insert to put a finished surface on a practice piece of 416SS.

Barrel dia. 1" , feed rate .001, @1100RPM, depth of cut .010 using no cutting fluid leaves me with a good finish. ( I will get some cutting fluid)

I would like to try a 222 insert, with a 1/32 radius and see if can get a better finish.

The larger the radius the smoother the finish, correct?

Will I have to change my lathe settings? Is there a rule of thumb.

Hal
 
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Hal said:
I have another question on getting a nice finish on ss.

The larger the radius the smoother the finish, correct?

Hal
Click to expand...

I feel this is generally the rule but certainly there are other factors to be considered. I use 1/32 radius on my carbide inserts except for some of the very small boring bars are smaller radius. I am not a machinist by trade so hopefully someone like Jackie will respond as well. If I want a real slick finish on a barrel I normally use one of the 3M abrasive pads to finish the job. Using a little lube will often improve the finish left by the cutting tool.
 
Hal said:
I have another question on getting a nice finish on ss.

I'm using a Diamond shaped (VCMW 221, 1/64 radius) tin coated carbide insert to put a finished surface on a practice piece of 416SS.

Barrel dia. 1" , feed rate .080, @1100RPM, depth of cut .010 using no cutting fluid leaves me with a good finish. ( I will get some cutting fluid)

I would like to try a 222 insert, with a 1/32 radius and see if can get a better finish.

The larger the radius the smoother the finish, correct?

Will I have to change my lathe settings? Is there a rule of thumb.

Hal
Click to expand...
I hope you mean 0.008 above and not the 0.080 you wrote.

On finishing stainless with carbide, the edge radius is much more important than nose radius. The sharper the edge radius the better.

Get a high sulfur cutting oil even if it is Rigid pipe threading oil.

Notice on this chart "other conditions".
http://shopswarf.orconhosting.net.nz/ansiinsert.html

Unless you are a really experienced machinist and have a rigid setup you will get a better finish on a hand-ground HSSCo lipped turning tool.

The center tool I would use for turning the tenon, the right hand tool to cut the crown, feeding from the bore out. The crown tool should be hand honed to a razor edge. And the right hand tool is good to cut the cone, feeding from the inside out.
2ilh5x3.jpg
 
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Jerry your correct I misread the feed chart, 80 TPI or 1.2 thousands.
Thanks for showing what the cutting tools should look like.
What does co lipped stand for.
Does the grind pattern on top of the tool act as a chip breaker, besides being a relief angle?

Hal
 
Hal said:
Jerry your correct I misread the feed chart, 80 TPI or 1.2 thousands.
Thanks for showing what the cutting tools should look like.
What does co lipped stand for.
Does the grind pattern on top of the tool act as a chip breaker, besides being a relief angle?

Hal
Click to expand...
HSSCo is for High Speed Steel Cobalt. It is a tool steel with Cobalt added to give it greater red hardness.

The lip on top causes a more positive cutting action. Like using a sharp knife instead of a dull knife. Whereas with most carbide inserts have a slight radius on the cutting edge which tends to tear the metal instead of cutting it. This tearing is more prevalent where the depth of cut is small. Read up on BUE (Built Up Edge). http://en.wikipedia.org/wiki/Built_up_edge

The surface that looks like a second lip in the background is because I can't see very well anymore, up close or distant.

There are carbide inserts made that have that really sharp cutting edge but they are not off-the shelf items since they require special consideration. A novice using these super sharp edge carbides would probably get in more trouble with them than not.
 
Jerry,

Thanks for the link to the shopswarf site. All sorts of good information there.

I've found that I can get a good finish with carbide tools if I push them. The spider chuck I made recently was made from a rough rusty lump of 6" rod end. I spun it at 700 rpm, took a cut deep enough to clean it up in one pass with a decent feed (I don't know what it was, but I know where the levers were set) and got a nice shiny finish. That was some sort of carbon steel mystery metal.

That said, my lathe (12x36 import) isn't rigid enough to achieve good accuracy with heavy cuts like that, so when precision is required I fall back to HSSCo tool bits. I find I can get a good finish with them at normal tool steel speeds and feeds, taking light cuts, and using a high sulfer cutting oil as you suggest.

Thanks for the pictures of the tools. If I get through my honey-do list in time, I'll head for the shop and grind a set like that to try out.

Fitch
 
Fitch

frwillia said:
Jerry,

Thanks for the link to the shopswarf site. All sorts of good information there.

I've found that I can get a good finish with carbide tools if I push them. The spider chuck I made recently was made from a rough rusty lump of 6" rod end. I spun it at 700 rpm, took a cut deep enough to clean it up in one pass with a decent feed (I don't know what it was, but I know where the levers were set) and got a nice shiny finish. That was some sort of carbon steel mystery metal.


Thanks for the pictures of the tools.
Fitch
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A couple of comments. On getting a good finish with carbide, when the cutting tool is under sufficient load, both in feedrate and speed (SFM-Surface Feet per Minute) you will get a good finish. Why? I'm sure you have read up on BUE by now. When you have a high feed and speed, the BUE does not exist meaning the carbide tool is doing all the cutting.

When you get down to shallow depth of cut, the BUE (workpiece material) is doing the cutting hence the tearing of the finish.

Now, on the HSSCo tools pictured above, first note that on crowning especially, you will get the best results facing from the bore to the OD. Meaning, the bottom clearance on the cutting edge must be very great.

Normal turning this clearance 7-12 degrees would be about right. Using this tool to finish the crown, I grind this surface to a radius of about 1/4".
 
JerrySharrett said:
A couple of comments. On getting a good finish with carbide, when the cutting tool is under sufficient load, both in feedrate and speed (SFM-Surface Feet per Minute) you will get a good finish. Why? I'm sure you have read up on BUE by now. When you have a high feed and speed, the BUE does not exist meaning the carbide tool is doing all the cutting.

When you get down to shallow depth of cut, the BUE (workpiece material) is doing the cutting hence the tearing of the finish.
Click to expand...

Yup.

Now, on the HSSCo tools pictured above, first note that on crowning especially, you will get the best results facing from the bore to the OD. Meaning, the bottom clearance on the cutting edge must be very great.
Click to expand...

Yup. I learned that the other day when I drilled a hole in th end of a piece of SS rod to practice crowning.

Normal turning this clearance 7-12 degrees would be about right. Using this tool to finish the crown, I grind this surface to a radius of about 1/4".
Click to expand...

I didn't try the radius but it sure sounds like a good idea.

The only carbide tool I've had good luck with turning slow is the Carmex lay down threading tool. That seems to work really well even as slow as 36 rpm. I don't use the full privile insert, I use one that has a range of thread sizes. I use it with Rigid threading oil. I usually take two or three passes at a particular setting and find the threads clean up very nicely. I'm planning to set my Savage up with a shoulder instead of the nut. That should permit me to stop threading under where the recoil lug will be with out having to run right up to the shoulder.

Fitch
 
frwillia said:
permit me to stop threading under where the recoil lug will be with out having to run right up to the shoulder.

Fitch
Click to expand...

A tip on threading to the shoulder. Set up the threading tool as you normally would. Move the threading tool to the place you wish it to stop in relation to the shoulder.

Then on the left carriage wing, use a magic marker and make a mark on the lathe bedway up against the carriage wing. When threading watch that mark instead of watching the threading tool to determine when to disengage the half-nut and retract the tool.

If you are watching the tool tip it is easy to get distracted by the chip coming off and the smoke from the cutting oil.

Practice the above a few times with the tool backed off a bit to build up your confidence.
 
A better, more positive method, would be to thread to an indicator on a magnetic base on the lathe bed against the carriage. With some practice one should be able to stop and remove the cross slide and chasing dial within .005" each time, which would be much more accurate than a magic marker mark. Just my two cents worth here.
 
Jkob said:
A better, more positive method, would be to thread to an indicator on a magnetic base on the lathe bed against the carriage. With some practice one should be able to stop and remove the cross slide and chasing dial within .005" each time, which would be much more accurate than a magic marker mark. Just my two cents worth here.
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Jkob, I'll challenge you to a duel on that one. Watching the indicator hand speed around is a distraction in its self. Watching the gap between the carriage wing and the mark on the way is just about a brain dead exercise.

Now if you are cutting something like 25-40 TPI and running at say 20 RPM the indicator might be best.

Try it both ways then decide, they will both work better than trying to watch the tool itself.
 
Hey Jerry thanks for the link to shopswarf.com There is a HUGE amount of info on there. I looked last night for several hours to find the formula to figure hole spacing. I found one that was way over my head. This chart has a simple number to multiply with to find the chordal length.

Thanks again

Joe Hynes
 
JerrySharrett said:
A tip on threading to the shoulder. Set up the threading tool as you normally would. Move the threading tool to the place you wish it to stop in relation to the shoulder.

Then on the left carriage wing, use a magic marker and make a mark on the lathe bedway up against the carriage wing. When threading watch that mark instead of watching the threading tool to determine when to disengage the half-nut and retract the tool.

If you are watching the tool tip it is easy to get distracted by the chip coming off and the smoke from the cutting oil.

Practice the above a few times with the tool backed off a bit to build up your confidence.
Click to expand...

I like the mark idea. I was considering, and may yet build, a mount for a microswitch. It could be on something that looks like my micrometer carriage stop or maybe just a magnetic base. I was planning to have the microswitch turn on a light.

An AA battery, an LED, and a microswitch ought to do that really well in a small self contained package.

I will have my buddy in Fridley MN see if Ax-Man has a microswitch that would work.

Fitch
 
I was in a local barrelmakers shop and he was setting back a 50 cal barrel, he used the hydraulic tracer on his DSG to pop the tool out each time he got to the shoulder. I told him it was cheating. He just smiled!!
 
threading

hi
if you are threading to a run out grove then you might try this.
turn your threading tool upside down start in the grove and thread away from the shoulder ( chuck running in reverse ) you can thread faster and get a better finish.??

regards tasy_ted:D
 
It is not that hard!

Guys it is not that hard to cut an external thread to a shoulder without a thread relief, it was taught to me the very first week of school about 38 years ago. Do you remember those ancient days before N.C.M. and then the later CNC MACHINES?

All you have to do is get a magnetic back for your .001 X 1” travel dial indicator. Set up to thread like you would normally do. Back off the cross slide about .050. Run in the compound slide one half of the double thread depth. Bring the point of the cutting tool to the shoulder leaving the amount of clearance you are comfortable with by advancing the carriage. Stick your dial indicator with the magnetic back on it to the way of the lathe with the stylus on the carriage. Here is the hard part, rotate the bezel until the zero is at the top. Move the indicator toward the carriage until you have three full revolutions of the needle, the rest is easy. Roll out your compound slide to zero, back off the carriage and set your cross slide to zero. Turn on lathe, when the appropriate number on the thread chasing dial is at the pointer engage the half nut, cut the thread. When the pointer of the dial indicator approaches about fifteen degrees to the zero on the last time around do the fun part. The fun part is roll out the cross slide and disengage the half nut simultaneously it is really easy to do this. There are just two things that you have to do the first one is, DO NOT LOOK AT THE THREAD! The second one is ONLY LOOK AT THE DIAL INDICATOR! Ok there are three, ROLL OUT the cross slide not in! Roll the carriage back toward the tail stock, re-zero the cross slide, dial in for your next cut with the compound and repeat. Repeat as required until the tread is finished. No cheesy tread relief, no turning off the lathe, no witch dance or any other such foolishness, just a very nice professional thread that tapers from the root to the major diameter at the end.

If you set up like I told you to do then as the thread gets deeper it moves closer the shoulder and you will end up with the amount of clearance that you chose in the beginning. If you don’t allow for this by manipulating the cross and compound slides during set up then you might run out of room to the shoulder. Don’t practice this for the first time on your new barrel!

When you are ready then you can step up and cut internal threads to a shoulder without a tread relief, like truing fractory actions and such. You don’t want to cut a thread relief in a factory action because that will be the weak point between the locking lugs and the barrel. On internal threads remember it is ROLL IN the cross slide not out.


Nic.
 
frwillia said:
I like the mark idea. I was considering, and may yet build, a mount for a microswitch. It could be on something that looks like my micrometer carriage stop or maybe just a magnetic base. I was planning to have the microswitch turn on a light.

An AA battery, an LED, and a microswitch ought to do that really well in a small self contained package.

I will have my buddy in Fridley MN see if Ax-Man has a microswitch that would work.

Fitch
Click to expand...
The best of all ideas is threading on a CNC lathe. Thread at 1500-2000 RPM, no problem.

Second best probably would be an automatic kickout built into the lathe. Not many of those lathes around are there?

Richards Custom Gun Shop http://richardscustomrifles.com/ offers what he says is a bolt-on. I haven't seen one nor a picture of one though.

The last resort is to make a "chicken slot" or thread relief. These look tacky and kind of mess up setting a barrel back if you ever need to.

Point is, the magic marker thing is just another method. It is simple and nearly foolproof. I've used and taught this method for years, and it works. You don't have to use it!!!!
 
I set up exactly like Nic does except I don't like multiple revs on the indicator. With the indicator zeroed at the top (zero pointing toward my work, 90° from bed) the indicator will have about .050" travel (1/2 dial rotation) before cross slide pullout/half nut disengagement. Just my preference so I don't get lost in indicator revs. I watch the carriage advance towards the indicator, it contacts the indicator, in a short time it arrives at zero, then twist/flip handles and levers. I end up finishing the roll out/disengagement about .005" after zero. Instead of trying to finish closer to zero I shoot for consistency rather than speed so my thread ramp out on the tenon looks nice and smooth. Setting up the cross slide handle in the same place for each threading job can be helpful too. Once you find a method you like it will become a comfortable routine and the tenon will be threaded in no time at all.
 
My problem with the dial indicator is that I use carbide and I get a much better surface finish when I speed up the RPM a bit. I'm going to try that magic marker trick, I can see how that could be easier to use rather than watching a rapidly spinning indicator:). Thanks for the tip JerryS!

My other thought was the automatic kickoff after just reading about them in the last week (here).
 
Method to the Madness

There is a reason for the three revolutions of the needle on the dial indicator. It allows the operator to gauge or time when to make the disengage / roll out move.

I use full profile carbide threading tools and cut 16 TPI threads at 125 RPMs with no problems at all. The surface finish is great and I don’t feel rushed or get dizzy from looking at the dial indicator or anything stupid like that.

I guess that if you only thread once in a while there is little need to learn to do it differently than you do now. I cut threads all the time, mostly 16, 18 and 20 TPI for barrel shanks; I have full profile inserts for those. For muzzle breaks I use a Circle Industries tool holder and carbide insert that allows threading from 20-44 TPI. For those fine threads you can speed up the RPMs if you want to increase production.

Nic.
 
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