Do you like your bump knurling tool?

[pinstripe]

I rang one of the US knurling tool manufacturers recently, and spoke with a very knowledgeable guy about knurling tools. I explained my needs, and was surprised that he recommended a bump knurling tool. He said that for infrequent home use, the extra wear/pressure on the machine was not an issue. He also said the finished result would be no different if you used the tool correctly, and that that the scissor or cut style tools would only be necessary if the diameter was below 1/4"

This goes against everything I have read online. People seem to hate the bump knurling tools, don't get results they are happy with, and don't feel good about what it does to the machine. It made me wonder if it's because these people are using old wheels that don't work well.

So what do you think? Are you happy with your bump knurler, or is it just taking up space in the drawer? I'd like something that is easy to use and gets good results. I'm making single parts most of the time, so I want it to work first time. I understand the importance of the diameter, so no need to go over that.

[Mcgyver]

imo it does put a lot of strain on things, as you have to give it quite a bit of force to create a decent knurl. I think its tough on the feedscrew and nut more so than the bearings, but its a lot of strain all around. There's the argument that on a decent machine, people have been doing it for years....and the counter is lathes have been wearing out for years.....point is if one way is tougher on the machine than the other it seems obvious what to do. With the scissor, you're also willing to crank on it, which is better for the knurl

I'd take the scissor over the bump....but I'm a cut knurl man myself

[MattiJ]

I have been always wondering is there any truth on claims how hard the bump tool is for lathe?
Decent-sized 11x24 lathe has bigger spindle bearings than average car wheel bearing and with load capacity probably thousands of pounds.
Maybe its hard on tiny tabletop machines but anything bigger than that I dont see problem. Feedscrew maybe but not the spinde bearing.

Cut tool is the way to go anyways if you want nice knurling, especially in anything harder.

[wierdscience]

I wouldn't say I am happy with bump knurling,but I don't have anything against it either.Most that have trouble doing never consider some needed math.Here is a good explanation of the process-

http://conradhoffman.com/knurling.htm

His method is similar to mine and seems to work well enough.It also helps to use knurls with as narrow a face width as possible and turn a bump out on the part and knurl it rather that just picking a spot and running the knurl in.

[enginuity]

I actually used my bump knurl tool in my last video on the brass screw. It worked okay. Mine is an import variety with wheels made from cheese. It will work better if you get proper wheels from a place like Accu Trak.

I used scissor type knurling tools for production stuff at work on CNC turning centers and they work great. Beautiful knurls, low forces etc.

It was suggested to me in my video comments that I really should look at cut knurling. I've never used cut knurling, but I think it suffers less from poor tracking and other common knurl problems. You can also make diamond knurls with straight wheels.

I haven't decided between a cut knurl tool or scissor knurl tool yet. I would suspect a formed knurl (with a bump or scissor tool) is slightly more durable - because the material is work hardened.

[pinstripe]

To the cut knurlers like Mcgyver and MattiJ. Is the cut knurling tool more fiddly to set up? Say you wanted to make one part on a manual machine, would you choose the scissor or the cut (assuming you had both).

I get the feeling that the cut is better for production work, but maybe not prototyping. The Dorian catalog has this to say.

Use Forming Knurl Tool for:

• Small to medium workpiece diameter
• To the shoulder knurling
• To centerless workpiece
• To band knurling application
• When high surface finish required

Use Cutting Knurl Tool for:

• Medium to large workpiece diameter
• To shoulderless diameter knurling
• To hard workpiece materials
• To long knurling application with live center
• For higher productivity

It seems like they are saying that the form knurling tool will give a better appearance. Does a cut knurl give a full raised diamond pattern, or only the outline of one?

As an aside, the Dorian catalog is a wealth of information about knurling.

http://www.doriantool.com/knurling-tools-catalog/

It's one of those online viewers, but there is a download button in the toolbar to download the PDF.

[Mcgyver]

To the cut knurlers like Mcgyver and MattiJ. Is the cut knurling tool more fiddly to set up? Say you wanted to make one part on a manual machine, would you choose the scissor or the cut (assuming you had both).

hands down cut....but I made my own that is easily adjustable. It has built in adjustment for the angle of the rolls, as well as a fine dovetail for height. I set bring it up to the revolving work, gently touch and fine tune the height (makes it easy to get it perfect), go to the end of the work, advance 15 thou and let it rip - full depth and a speed.

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

[pinstripe]

I actually used my bump knurl tool in my last video on the brass screw. It worked okay. Mine is an import variety with wheels made from cheese. It will work better if you get proper wheels from a place like Accu Trak.

I haven't watched that one yet, but I will be soon. Accu Trak is what I am looking at. They seem to be well regarded, and their prices are reasonable for a quality tool.

It was suggested to me in my video comments that I really should look at cut knurling. I've never used cut knurling, but I think it suffers less from poor tracking and other common knurl problems. You can also make diamond knurls with straight wheels.

Cut knurling seems to be the preferred option in production. Still not sure if it's the best way to go for one part. Accu Trak's catalog has some tips on page 2 (4 of the PDF). I can't paste them here because the PDF doesn't allow it. Short story, ram the die into the blank hard to get it started. On CNC, slow down spindle for initial contact to avoid double-tracking, then speed up as soon as it's cut into the blank.

[Jaakko Fagerlund]

What I've used a cut-style knurler, it had one screw to adjust the angle of the knurls and it was graduated in workpiece diameter, so it was easy to set up, touch off, feed in the proper amount for the current rolls and engage feed.

The difference of course being that the cut knurl is cut - it doesn't raise the material like form knurling tool does. But in my use I need knurls for aesthetics or for hand wheels etc., so I don't need the diameter to grow and cut knurling is easier and allows for faster work.

[J Tiers]

It seems hardly possible for Dorian to have created a more obnoxious and inconvenient way to view their catalog.....

Anyway......They, and others, are firmly in the group that says diameter matters. The grumpy old machinists say that only "home shop Harry" type amateurs, screwing around in their basement without a clue using some lightweight hobby lathe, worry about diameter, "just jam the knurl in and it will work", they say.

Seems obvious that when you end up with a good knurl, that there is a definite diameter and number of knurl points around the part. I suspect that if you DO "just jam it in" that the knurl probably adjusts itself a bit, skidding around and making a knurl that is not quite the same circular pitch as the knurl itself. Alternately, the knurling may be slightly imperfect in form, just enough so that it does come out right. So both are right to some degree, but for an absolutely perfect knurl it would need to be on the right diameter.

The force is very large if you "just jam it in". If you tried to press that pattern into the metal it would take a great deal of pressure. Since it is rotating, the pressure is spread out over time, but the material work-hardens during the knurling, and presumably gets harder toward the final forming.

The advice that small machines can use the bump knurling tool seems backwards. A big heavy machine and a small knurling tool makes sense, the force is small compared to what it can take. A small machine is not built to have that much cross-force on the carriage.

Plus, there is the workpiece to be considered also. A large machine often means a larger workpiece, that can stand the pressure without bending or deflecting. Small workpieces would not stand the side pressure, and they are the size more typical on a small machine.

The whole argument seems wrong-headed and backwards.

I very seldom do any knurling, but I try to start at the end and feed the knurl across the area, so that the forming occurs at the leading face of the knurl, and not all across at once. Lowers the pressure. A Logan is not a tiny and light machine compared to others, but it feels wrong to crank in enough pressure to get a quarter-inch wide knurl to do a good form even on 1018 when plunging it straight in.

[_Paul_]

Personally I dont like bump knurling IMO it puts unnecessary strain on my Boxford's headstock bearings and cross slide nut, even when fitted with good quality knurls using my bump type I can hear the lathe slow down and start to groan... knurling small or delicate components is also out of the question as it pushes away from the knurler unless you want the added inconvenience of using a centre but even that may not work with some smaller components.

I like a clamp and/or scissor type knurler for small items and made a cut knurler for bigger items, IMHO the cut knurler is more fiddly to setup but then that could be down to my shop made versions idiosyncrasies.







For smaller parts I prefer this one which is a larger shop made copy of Hemingway's knurling tool.



Paul

[metalmagpie]

As an aside, the Dorian catalog is a wealth of information about knurling.

http://www.doriantool.com/knurling-tools-catalog/

It's one of those online viewers, but there is a download button in the toolbar to download the PDF.

Here is a direct link to a Dorian knurling PDF:

http://www.doriantool.com/wp-content/uploads/dorian_tool_Knurling-2012.pdf

metalmagpie

[TGTool]

I use a scissors knurling tool and it always works - without any calculation for diameter. Putting a lot of pressure on the clamp seems like the key to getting it to register. I'll engage it, tighten the nut, turn the lathe on and off to get a few revolutions and see what the pattern looks like, If it's not a clear pattern (mismatch of knurl pitch and work diameter) it just needs more cranking on the nut. Oil it up, crank it down and she'll be good. If it's a long knurl, longer that the wheel width, I'll need to traverse down the part and with the pressure and resistance this sometimes means that I also need to push the scissor along in addition to moving the carriage. Is that a defect in the process? Dunno. I've just learned what to do to make it work and it always works for me. I suppose that defines me as a home shop old fart machinist but in my defense, I do have a business and send knurled parts out to customers so I need to be sure they look good. Sending out a knurled nut with a multi track wimpy scratch pattern just seems amateurish.

[J Tiers]

When you tighten down the tool, you are changing the diameter. With a reasonably fine knurl, it's a pretty small difference that gets to a proper size. A few extra flakes of metal, and there you are.

[Mcgyver]

P IMHO the cut knurler is more fiddly to setup

its not you its the tool I had the same issues with the first one I made. To avoid the fussiness, I geared the two wheel mounts together so adjustment for diameter is quick and easy. As well there is fine height adjustment. imo a QCTP height adjustment is insufficient as there needs to be an easy way to adjust height after adjusting for diameter and bringing the tool into initial contact with the work.

Building in those two adjustments is a lot more front end work, but making great knurls becomes plug and play