Problem Knurling Stainless Steel

[gakor]

I'm trying to knurl a part made of T303 stainless steel. I'm using an Acu Trak bump knurl holder with one high speed steel 96DP 3/4" dia. 1/4" wide straight knurl wheeel. I can only knurl about 0.0050" deep and the machine shuts off. I guess overload kicks in.

The part has to be made out of stainless steel, but I can use any type. Is there a more suited type of stainless steel for knurling? Maybe using a knurl, other then Acu Trak, would give better results?

I've tried to cut little grooves on the part to releive some pressure, but that didn't get me too far, although it did help a little. Altogether, its still not good enough. Any suggestions? How can I overcome this problem?

Thanks ahead.

[HuFlungDung]

I don't know much about knurling on an automatic lathe, but its really tough going on a manual knurl if you begin with the knurl full width over the part. Its best to begin on a narrow sliver at the outboard end, about .1" wide, go in fairly deep and fast to attempt to get the knurl tracking immediately on the second revolution. Once a good track is established, back off the pressure to a moderate depth position and begin the lateral feed. Ideally, complete the knurl in one pass.

If starting the knurl almost off the end of the part is not possible, the next best solution, IMO, is to tilt the toolholder a little bit, to make the leading edge of the wheel dig in and do most of the work.

303 stainless may want to fleck off due to its free machining qualities. 304 would likely be better. It will harden up a bit too, due to the cold working of the knurl, but 96Dp is pretty fine. If you find the magic depth setting, it should knurl up quick in one pass.

[SwissType1]

Bump knurling should generally be avoided when knurling tough materials on a CNC swiss because of the high side-load it applies to the guide bushing. It is also more likely to deflect the part.

I would recommend using a low profile, adjustable straddle knurl from the gang slide. The convex style accu-trak knurls should be adequate for the application as they allow you to feed through in the Z-axis.

www.genswiss.com/knurltools.htm

[gakor]

Would anyone know if I can use a setup like this (like in the picture) for straight knurling? Will the wheels match/line up (as in, will the teeth fall into the same tracks, or will they go in between grooves?)?

[yoopertool]

I do a considerable amount of knurling on all kinds of stainless and I agree with SwissType1, dont mess with bump knurling. The knurl quality and repeatability of an adjustable straddle knurl tool will be much better. I preffer to knurl on 17-4 stainless, but get good results on 303 as well. If you do venture out and get yourself a straddle knurl tool, there are a few things I do to make my knurls look good. They are:

-for a 96dp knurl, set the distance between the wheels .015" smaller than the pre-knurl diameter.
-Use LOTS of good quality coolant. I prefer oil based.
-Take your time to make sure that the tool is centered on the stock.
-Try different appoaches. You can feed onto the part in either Z or X. Both have their advantages.
-Put a small chamfer on the edges of the wheels. About .02" will do.
-Dont feed too slow. I typically knurl abour .5" material with 750rpm and feed around .015ipr.

Good luck! I hope it all works out for you!

[SwissType1]

Would anyone know if I can use a setup like this (like in the picture) for straight knurling? Will the wheels match/line up (as in, will the teeth fall into the same tracks, or will they go in between grooves?)?

Yes, you can perform straight knurling using a 2 die setup like above. The key is to get a decent bite in the first few revolutions of the stock. The dies will follow the paths they made after that, even when feeding in Z.

[JAB Mach]

Knurling help needed (desperately)- Trying to find helpful instruction in reading all of the posts. I have a 20" long 4" diameter cylinder 304, using a convex wheel and I can't get the pattern to line up. I can get the lower knurling wheel to track properly but can NOT get the upper wheel to align or track properly. I have wasted a day trying to do this changing the feed, tool is on center, have tried angling the tool. It is a 10 TPI knurl. I am turning the diameter in multiples of .0318. The knurling tips on the 3/4 inch wheel I am using are .100 apart. Need specific helpful instruction to get both of the wheels to track properly.

[HuFlungDung]

I don't suppose angling a convex tool is going to really be much advantage because its still not going to present a corner to the work. I think you need an extreme pressure advantage to get the knurl to track.

I don't know if you've got extra length to work with on your stock, but you might try cutting a groove something like 1/4" wide, and start the knurl centered over the groove. So this should give the knurl an easy bite on two corners to get a chance to track. Feed in fast and hard (in less than one revolution) and see if you can get the pattern established. Once established, then back off to a more reasonable depth and try the longitudinal feed.

[kingfisher]

I do a considerable amount of knurling on all kinds of stainless and I agree with SwissType1, dont mess with bump knurling. The knurl quality and repeatability of an adjustable straddle knurl tool will be much better. I preffer to knurl on 17-4 stainless, but get good results on 303 as well. If you do venture out and get yourself a straddle knurl tool, there are a few things I do to make my knurls look good. They are:

-for a 96dp knurl, set the distance between the wheels .015" smaller than the pre-knurl diameter.
-Use LOTS of good quality coolant. I prefer oil based.
-Take your time to make sure that the tool is centered on the stock.
-Try different appoaches. You can feed onto the part in either Z or X. Both have their advantages.
-Put a small chamfer on the edges of the wheels. About .02" will do.
-Dont feed too slow. I typically knurl abour .5" material with 750rpm and feed around .015ipr.

Good luck! I hope it all works out for you!

Coolant/oil content is so important when it comes to SS. If you are running water soluable make sure the mixture content is higher then 13. If you can run straight oil...... you are better off.

[PixMan]

If you're on a true Swiss-type machine, you should only run pure cutting oils. Everytime I've seen people running water-based coolants, nothing but troubles with electrical and rust issues follow...sooner or later. Oils are what they're built to handle.

Back to the OP's problem: If your machine is stalling at only .005" into the part, you are probably running so slow that you're below the spindle drive's recommeded RPM range. No way should that stall a spindle, and none of the other methods mentioned are going to act any better on it.

[HSPMInc]

Knurling help needed (desperately)- Trying to find helpful instruction in reading all of the posts. I have a 20" long 4" diameter cylinder 304, using a convex wheel and I can't get the pattern to line up. I can get the lower knurling wheel to track properly but can NOT get the upper wheel to align or track properly. I have wasted a day trying to do this changing the feed, tool is on center, have tried angling the tool. It is a 10 TPI knurl. I am turning the diameter in multiples of .0318. The knurling tips on the 3/4 inch wheel I am using are .100 apart. Need specific helpful instruction to get both of the wheels to track properly.

Try playing with RPM. If you're 100% sure that centerline is on then it's either speed/feed or pressure. Try leaving a little more material or push a little harder with the knurler(lower your X, not feed). Sometimes you just have to push harder to get both wheels to track together.

[petriej]

Can you find a cut knurl that's that pitch. If so, then maybe look at one of these from Eagle Rock Tooling



No deflection and you can run through the back to whatever length you need. OD depends on which model you get.