Can I get away with knurling over rust?

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

shild
Posts: 293
Joined: Mon Jan 22, 2018 11:58 pm

Can I get away with knurling over rust?

Post by shild »

Going make some knobs from round stock with some surface rust. It's already indicated in a 4-jaw. Do I have to do a pass to get rid of the rust or can I get away with just knurling the rust off?
User avatar
Builder01
Posts: 726
Joined: Mon May 18, 2015 5:26 am
Location: Erie, PA

Re: Can I get away with knurling over rust?

Post by Builder01 »

You might try a bit of emery cloth on the rust. Then knurl. I would not want to push rust into the grooves of my knurler wheels.

David
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Can I get away with knurling over rust?

Post by Harold_V »

The other consideration, assuming you care about uniformity, is that material isn't generally real round. If the material in question is hot rolled, you'd be far better off to take a skim cut, if for no other reason, to create a truly round surface. The knurl would look a lot better if it was uniform in depth, plus, if you ever had to grip the part for any reason, the knurl would then be concentric with the balance of the part, and could be used with soft jaws for work holding, assuming it might be necessary.

I would not choose to knurl over rust unless it was extremely thin, and could be wiped off with a rag. Beyond that, I'd take a skim cut. But that's me. YMMV.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
rkcarguy
Posts: 1730
Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Can I get away with knurling over rust?

Post by rkcarguy »

I'd get rid of the rust, otherwise it will be pushed into the knurl and it will repeatedly rust...if that is a concern.
Should be able to sand or file it off so you don't have to take down your knurling setup.
shild
Posts: 293
Joined: Mon Jan 22, 2018 11:58 pm

Re: Can I get away with knurling over rust?

Post by shild »

Alright thanks guys! Got another question, how fast is too fast when knurling? The piece of stock is 1" diameter and seems to be cold rolled. Was playing it really safe and only going about 100 rpm but it's safe to go much faster isn't it?
RET
Posts: 960
Joined: Wed Jun 07, 2006 8:36 am
Location: Toronto, Canada

Re: Can I get away with knurling over rust?

Post by RET »

Hi Shld,

I run knurls very slowly because you have to put a lot of pressure on the knurl to do a proper job and the knurl axles are only plain bearings. The clamp type works at a lower pressure, but even so a slow speed is best.

Using a knurl is something like threading, so if you play with the power feed rate you can get a setup that works to give a better and smoother result. What also helps a lot is not to have the knurl wheel axes parallel to the work, but to angle the knurl toolholder so that the greatest pressure is on the trailing edge of the setup.

Just a few of the things I have found out by experience.

Richard Trounce.
rkcarguy
Posts: 1730
Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Can I get away with knurling over rust?

Post by rkcarguy »

It's been awhile since I've knurled, but I always ran a very low rpm, fairly aggressive feed, and plenty of pressure on the knurling tool with lots of oil or coolant. The knurl will turn out amazing if you keep the tool flooded with oil/coolant so the metal shavings don't recirculate through the tool.
Do you have a piece to practice on?
rkcarguy
Posts: 1730
Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Can I get away with knurling over rust?

Post by rkcarguy »

+1 to Richards comment, having the tool slightly angled lets the knurling tool work its way into the cut. I've gone backwards in some cases when I was knurling up to a step up in diameter so the knurling would be uniform across the part.
User avatar
Builder01
Posts: 726
Joined: Mon May 18, 2015 5:26 am
Location: Erie, PA

Re: Can I get away with knurling over rust?

Post by Builder01 »

I start the knurl by turning the chuck by hand until I know for sure that I am not "double knurling" the pattern. Then, slowest rpm and then I feed by hand. As rkcarguy says, a coolant flood to prevent displaced metal from going around the knurling wheels and getting pushed back into the work. Compressed air also works to keep the knurling wheels clean. A diamond knurl is finished when the peaks of the diamonds are "pointy". As other have mentioned as well, angling the knurling tool from the work axis works well also.

David
rkcarguy
Posts: 1730
Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Can I get away with knurling over rust?

Post by rkcarguy »

The diamond knurl can be less than wonderful on the hands, I used to run mine a little shallow or take a little cut to take the tops off the diamonds after I was done. My tech school tap handle project was fully knurled and after tapping several holes my hands were becoming hamburger. If its a knob where you need grip and only adjust it occasionally a full knurl is probably ok.
RET
Posts: 960
Joined: Wed Jun 07, 2006 8:36 am
Location: Toronto, Canada

Re: Can I get away with knurling over rust?

Post by RET »

Hi,

Just a quick addition.

The power feed is right when the ridges on the knurl wheels land precisely in the corresponding valleys on the work. This will produce relatively sharp points on the finished knurl. If coarse wheels produce a more aggressive finish than desired, either use a finer knurl pair or reduce the pressure on the part to get a "softer" surface. You could also touch the surface up with a file to get the desired finish.

Richard Trounce.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Can I get away with knurling over rust?

Post by Harold_V »

RET wrote: Fri Aug 31, 2018 9:09 pm Using a knurl is something like threading, so if you play with the power feed rate you can get a setup that works to give a better and smoother result. What also helps a lot is not to have the knurl wheel axes parallel to the work, but to angle the knurl toolholder so that the greatest pressure is on the trailing edge of the setup.
I tend to not agree with that assessment. Here's why.
As you alter the relationship of the rollers to the work piece, they present more and more surface area to themselves, assuming the trailing edge is the deepest point. That leads to feed marks in the knurl, and requires greater pressure because you're trying to displace a greater percentage of material as the stock revolves (larger surface area being displaced). My choice has always been to ensure that the knurl is, for all practical purposes, parallel to the work. That way, much the same way a centerless grinder works, the corner of the tool does the work, establishing depth, leaving the balance of the roller to "spark out", for lack of a better description. Knurling pressure seems to be lower, and the end result is quite good. Also, if you knurl to a given length, the knurl will be at full form right to the end, unlike when the tool is set at a slight angle. Looks much better.

By using a knurling tool in this fashion, you can select a feed rate that you like (I like a reasonably fast feed), and use reverse to change direction. If the rolls are parallel, there are no feed marks, and running the knurls in both directions tends to yield a more consistent knurl and diameter.

I also like to start my knurls on the edge of a part, assuming it's knurled to the end. By picking a small portion of the corner (about 1/16"), and plunging the tool rapidly in to the spinning part, a good knurl is almost guaranteed. Once the knurl is complete, I then chamfer the edge, generally slightly deeper than the knurl in question. The end result is very pleasing, and comfortable to grip.

Knurling creates a huge amount of heat. Slow spindle speed is desirable, while a reasonably fast feed tends to yield better results, especially if one is knurling materials that work harden easily. Like stainless.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Post Reply