Knurling 303 issue, fine knurl with stripe. How to mitigate it?

[WobblyHand]

Made @mikey's straddle knurler a while back and have made some ok knurls in brass, aluminum and 12L14. I used 25 TPI Formroll knurls.

I have some 303 stainless and would like to make a new razor handle. I chose my 30 TPI knurls to do the knurling. The knurls came out kind of strange, there's almost a darker spiral down the piece. (About 9 turns) The piece was held by a ER32 collet and a live center at the tailstock. For the first time (was this my mistake?) I used the lead screw to feed the knurler towards the chuck. I got a fine knurl going then engaged the lead screw. Used a sulfur based cutting oil. Can someone point me in the right direction? I haven't finished the piece yet, but attached it to the razor head. It needs to be cut to length and have some additional features added. The spiral, which was much much darker when the knurls were cut, is a visual distraction. I scrubbed the handle 3 times - there's still a spiral

This appears to be double knurling? (Not tracking?) The knurl seems really fine. Then I need more initial pressure? Any other tips for knurling 303?

Cut of the knurls and try again? The handle is a little large, so I could make it thinner.

 

[Aukai]

Power feed, low RPM, single phase power supply? If it were me I'd cut, and try again, and see what fixes are suggested.

 

[benmychree]

Knurls are sensitive to part diameter, they do not like odd diameters; diametral pitch knurls like fractional diameters while circular pitch knurls like odd diameters. I like to start the knurl on about half the width of the knurl roll, and take it to full impression, then switch on the feed and take it full length.

 

[WobblyHand]

Power feed, low RPM, single phase power supply? If it were me I'd cut, and try again, and see what fixes are suggested.

Could have used lower RPM, (but didn't) didn't even think about that. Yes, used the lead screw to feed. Single phase AC (but DC motor)
I'll cut off the knurl and give it another go.

 

[WobblyHand]

Knurls are sensitive to part diameter, they do not like odd diameters; diametral pitch knurls like fractional diameters while circular pitch knurls like odd diameters. I like to start the knurl on about half the width of the knurl roll, and take it to full impression, then switch on the feed and take it full length.

Ah, starting on 1/2 width... That's a good idea to be able to start the knurl. I'll try that. Thanks!

 

[Aukai]

If my other lathe was run too slow it would surge, your stripes look very evenly spaced. See what is suggested for fixes, after you skim it.

 

[KevinM]

I may not have any suggestions to help you but these questions may shed some light on the issue. Do your knurling wheels have a bevel on the edges? Is your knurling tool perpendicular to the workpiece? Is your knurling tool a scissor type or a pressure type? If it is a scissor type is it on center? Is your cross-slide locked? I have had a scissor type move the cross-slide when knurling.

 

[mksj]

I only have done knurling with manual feeds, and I can feel the knurler advance. If advanced too slow or too fast with an auto-feed I would expect to see some form of uniform repeating pattern. As others mentioned, diameter of the stock relative to the knurler TPI can cause issues if there is a mismatch. Might want to try on some scrap stock of the same diameter. I normally knurl at around 160 RPM, and have been knurling in one pass, but can take some trial an error to dial it in. Also using plenty of oil and keeping everything clean.

 

[Forty Niner]

Search for "Conrad's Easy Knurling Method"
I could post it but think it is easy to find and I don't have rights to it.
Use the method to determine what diameter your material should be for your knurls.

 

[WobblyHand]

Knurls are sensitive to part diameter, they do not like odd diameters; diametral pitch knurls like fractional diameters while circular pitch knurls like odd diameters. I like to start the knurl on about half the width of the knurl roll, and take it to full impression, then switch on the feed and take it full length.

@benmychree had it. Needed to start at about half width. Easier to get the knurl going correctly so it will track. With 1/2 knurl width in contact with the part, I increased the pressure until I got a proper tracking knurl, then turn on the feed. Slow RPM, oil wheels as necessary. Worked beautifully. No voodoo on matching diameters and TPI - just pressure and starting the knurl with only half the wheel widths engaged. Part started at 0.500", but I turned it to clean it up and knurl, then I cut off the knurl and tried again. End diameter = ?

The knurl wheels I have are circular pitch, which apparently are good for straddle knurlers and often start correctly (according to Form Roll Die). I have the EQ series knurls in 25 and 30 TPI. They are 1/2" OD, 3/16" ID and 1/4" wide. I ordered beveled wheels as a special order.

Straddle type knurler (arms clamped across diameter) attached to a plinth on the backside of the cross-slide. This setup lets you see what you are doing and allows easy oiling of the wheels.

Made my razor handle too. Original was a bit too skinny for my liking. Came out good enough to use and not too ugly

Thanks for everyone's help!