Do you like your bump knurling tool?

[wierdscience]

Unless I missed it no one has mentioned knurl roll width as being a factor which it is.There are the Armstrong type rolls which are 3/8 to 1/2 wide and the Landis? Type that are only 1/4" wide.I prefer the narrower ones if possible since they take far less pressure to accomplish the same job.

Another tip for bump knurling is,if you are starting on the end of a bar,cock the knurling tool around to a 30-40 degree angle and run it into the outside corner and let the knurl go to full depth there.Then swing the knurling tool back to it's normal position perpendicular to the work,with about a 1 to 1-1/2 degree lead in the direction of feed.Doing that,your rolls will pick up and time off that corner easily and you can go right to knurling without coaxing the rolls into time.

[wierdscience]

I'm on the other side of the great knurl debate from Darin, I've never worried about the diameter and get perfect knurls. Mind you, I like fine knurls....perhaps it matters on a coarse knurl on small diameters

I don't worry about it either,I just use a pocket calculator to make an educated guess at the diameter.And that's all that is really needed is a close guess.Knurling isn't as critical as gear cutting,since the knurls will self compensate somewhat.All I do is check the knurl pitch with a thread gauge.Then do some simple math,as an example,if I want a roughly 1" OD with a 16 pitch knurl I will do the following- 1.00 x 3.14 = 3.14 / .0625 = 50.24 "teeth" on the finished part. Since 50.24 is not a good "tooth" count,I take 50 x .0625 = 3.125 / 3.14 = .995". Easy,takes about 5 seconds without dicking around with spread sheets and knurl calcs.

Here's another Knurl calculator that works simply and agrees with my result.

http://www.cgtk.co.uk/metalwork/reference/knurl

[PStechPaul]

I haven't tried knurling yet, but I think I will do so soon. I have a small cheap one for a mini-lathe and a larger one that came with a set of QCTP holders from LMS that I bought at Cabin Fever in 2016. I do have some concerns about doing it on my relatively flimsy HF 9x20, however. From the Dorian PDF it seems that the knurling tools are designed to work for diameters in increments of 1/32 or 1/64 inch. Thus the diametrical pitch (or perhaps the circular pitch) will match the final diameter of the finished knurl, which may not be the same as the unfinished diameter of the piece. I surmise that the teeth of the knurling tool are machined such that it works best on a certain range of diameters, similar to gear cutters. But the tooth form is not critical for knurling. It seems that knurling tools are made for diameters up to 1" and as small as 5/64", depending on TPI and width of tool.

The knurl forming process causes an increase in overall diameter, whereas the cutting process does not, so calculations and TPI may be different. I think I would prefer the scissors type tool or one that has an adjustable gap between the wheels that reduces the force needed to form the knurl. I don't know how the double wheel forming tools synchronize their rotation to the knurl, although for a diamond knurl using one right-hand and the other left-hand it would not matter.

[metalmagpie]

I don't worry about it either,I just use a pocket calculator to make an educated guess at the diameter.And that's all that is really needed is a close guess.Knurling isn't as critical as gear cutting,since the knurls will self compensate somewhat.All I do is check the knurl pitch with a thread gauge.Then do some simple math,as an example,if I want a roughly 1" OD with a 16 pitch knurl I will do the following- 1.00 x 3.14 = 3.14 / .0625 = 50.24 "teeth" on the finished part. Since 50.24 is not a good "tooth" count,I take 50 x .0625 = 3.125 / 3.14 = .995". Easy,takes about 5 seconds without dicking around with spread sheets and knurl calcs.

Here's another Knurl calculator that works simply and agrees with my result.

http://www.cgtk.co.uk/metalwork/reference/knurl

What is the 3.125 number?

[wierdscience]

What is the 3.125 number?

The circumference of the resulting .995" work piece diameter.The first calculation gives an idea of how many "teeth" the desired knurl will have,in the example 50.24.Since 50.24 isn't an even count we round it down to 50 then multiply by the knurl pitch which in this case is 1/16 or .0625 and we get 3.125 and then divide that by Pi which is 3.14 and the result is a .995" diameter.

Note that the diameter of the finished Knurl will be larger than 1.00",how much depends on the knurl depth which can be anything depending on the desired result.

[thaiguzzi]

Slightly OT, i've got the Hemingway Marlco copy clamp type to make. Have the drawings and material kit sat around a while now. Drawings state using 3/16" wide knurls, i was going to modify this to 1/4" wide.
I have two "bump" type knurlers i've used for decades (with varying degrees of success), both with a swivelling head and six knurls. One is Jones and Shipman, the other is Pratt and Whitney. Knurls are still in great condition, ie sharp.
My question is, if i make a jig/holder for my T&CG, can i grind down the above knurls from their 3/8" width to the 1/4" i want without damage to the knurls themselves? I don't mind the time taken, or should i just buy new knurls?

[J Tiers]

Unless I missed it no one has mentioned knurl roll width as being a factor which it is.There are the Armstrong type rolls which are 3/8 to 1/2 wide and the Landis? Type that are only 1/4" wide.I prefer the narrower ones if possible since they take far less pressure to accomplish the same job.

...

I mentioned it in passing... saying I'd like narrower ones since the existing ones take a lot of pressure.

The ones I have seem to be in between. I didn't measure, but they appear to be between 1/4 and 3/8. Nowhere near 1/2". McMaster shows knurling tools with wheels of 5/16" which is likely the size I have. They still take too much pressure for the 10" machine.

The link to Dorian tool shows some that are as narrow as 0.156", with 0.187 and 5mm also, as well as 6mm and 1/4", plus 0.375. The 0,156 would probably be fine for bump knurling. Otherwise, the floating clamp-type holders seem a good plan. I DO have some straight-sided knurls, and could therefore make a cut knurl tool, but it seems like a lot of work for as much use as I'd get out of it.

[TGTool]

So you are effectively changing the diameter. Instead of calculating it and starting with the right diameter, you are adjusting the wheels until they are set at the right diameter to track correctly. JT beat me to it

Well, everything I make must be above average. If oversize stock can be squeezed down to the right diameter, what does correctly sized stock get adjusted to?

[wierdscience]

I mentioned it in passing... saying I'd like narrower ones since the existing ones take a lot of pressure.

The ones I have seem to be in between. I didn't measure, but they appear to be between 1/4 and 3/8. Nowhere near 1/2". McMaster shows knurling tools with wheels of 5/16" which is likely the size I have. They still take too much pressure for the 10" machine.

The link to Dorian tool shows some that are as narrow as 0.156", with 0.187 and 5mm also, as well as 6mm and 1/4", plus 0.375. The 0,156 would probably be fine for bump knurling. Otherwise, the floating clamp-type holders seem a good plan. I DO have some straight-sided knurls, and could therefore make a cut knurl tool, but it seems like a lot of work for as much use as I'd get out of it.

I've got some that are 3/8 wide,but only have a 3/16 wide band in the middle that knurl.Same amount of bearing surface on the pins as the full width ones,but take much less pressure to knurl with.

Armstrong apparently made different sized knurls and knurling tools meant for larger or smaller lathes.I have one tool knocking around that has a 4" long 3/4 x 3/8 shank and tiny little 3/8 OD x 1/8 wide knurls.Then I also have a big one that has a 1 x 2" shank about 8" long with the big 1/2 wide knurls.My go to at work however is the Aloris tri-roll set,purely for the convenience.

[_Paul_]

I did it as a build piece in HSM so made it nice and shiney

Lovely work indeed sir! as you say trying to set the height using the threads on a tool holder really is a challenge and I do like the idea of gearing the two knurls together, which issue of HSM was it in?

Paul

[_Paul_]

Slightly OT, i've got the Hemingway Marlco copy clamp type to make. Have the drawings and material kit sat around a while now. Drawings state using 3/16" wide knurls, i was going to modify this to 1/4" wide.
I have two "bump" type knurlers i've used for decades (with varying degrees of success), both with a swivelling head and six knurls. One is Jones and Shipman, the other is Pratt and Whitney. Knurls are still in great condition, ie sharp.
My question is, if i make a jig/holder for my T&CG, can i grind down the above knurls from their 3/8" width to the 1/4" i want without damage to the knurls themselves? I don't mind the time taken, or should i just buy new knurls?

When I made my cut knurler the only straight knurls I had lacked a really crisp edge so I took them for a ride on my old T&CG and probably took off around 1/16" to get an edge that I liked but I was lazy with the setup and simply put them on the mag table with a parallel as a stop so grinding down did take a little time.

[thaiguzzi]

Yeah, thanx Paul. Haven't got a little mag table for my Stent (always looking...), so it's make a fixture to hold the knurl in the 3 axis tool holder.

[pinstripe]

Thanks all. I ended up ordering the scissor/straddle knurl. I think the gentleman at Accu Trak was trying to save me some money by recommending the bump tool. He was probably right, and it would have been fine on my lathe, but I feel more comfortable with the scissor.

Incidentally, everyone I dealt with at Accu Track was excellent. They had no problem shipping to a freight forwarder and taking an overseas credit card. Some companies in the US aren't so easy to buy from.

There is a video of their factory on YT. Skip to 2:30 for the good stuff.

[Tim Aldrich]

I have both bump and scissor knurling tools. When I'm making one or two simple things, such as a thumb screw, and just need something to grip, it's easiest just to drop the bump knurler into the tool holder. I make a lot of simple fittings for my day job and don't care what the knurl looks like as long as it's sufficient to aid in grip. Long knurls (like a hammer handle) or knurls that I want to look good will be done with the scissor knurling tool.

[pinstripe]

Quick follow-up. The Accu Trak knurler is very nice. I only got a chance to play with it today. I was too impatient to do all the calculations, so I figured I would start with aluminium to avoid damaging anything. Stock is 1" with convex 1mm wheels.

From right to left. First attempt was too tight and I ended up with a crunchy mess of aluminium and oil. Second attempt was better, but still a little crunchy. Third attempt made no chips, and looks good to me.