How to Properly Knurl this Part

[Crashmaster]

I need to bump knurl this part on my CNC lathe and try to hold a tolerance of +/-.001. I am using a straight knurl but am having a problem staying consistent. I have been dwelling when I reach depth for 5 seconds and have a feeling that is not the best way to go about it. If anybody has any suggestions that would be great. I realize knurling is a trial and error type of thing but I don't even know if my speeds/feeds are anywhere close to where they need to be. Thanks.

[Crashmaster]

OOPS! That file I attached was horrible. This one should be better.

[g-codeguy]

I was hoping to see some intelligent answers here. Don't know if it is because we seldom get a knurling job, but knurling has always been a PIA for me. Most are done using X-axis to push the knurl into the part. I assume this is what you call "bump knurling". We did straddle knurl one job. Broke the knurling tool twice.

Picked up a used Hardinge not long ago that came with a knurling tool I hadn't seen before. Looks like you cut with the edge of the tool, and feed in from Z-axis.

I know that pitch and diameter are tied together, but that knowledge doesn't seem to help me much. Must admit that knurling is a subject I never researched.

Surely there must be someone on this forum that could enlighten us!

BTW, what do I need on my computer to open a .dxf file? Autocad? Know a .dxf file can be imported into MasterCam.

[rustamd]

would probably help if you posted picture version of your dxf, since its kind of extra pain to download it and open in acad or other software, specialy on older computers, it takes quite awhile to load the software.

[rustamd]

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[rustamd]

Originally Posted by g-codeguy I was hoping to see some intelligent answers here. Don't know if it is because we seldom get a knurling job, but knurling has always been a PIA for me. Most are done using X-axis to push the knurl into the part. I assume this is what you call "bump knurling". We did straddle knurl one job. Broke the knurling tool twice. Picked up a used Hardinge not long ago that came with a knurling tool I hadn't seen before. Looks like you cut with the edge of the tool, and feed in from Z-axis. I know that pitch and diameter are tied together, but that knowledge doesn't seem to help me much. Must admit that knurling is a subject I never researched. Surely there must be someone on this forum that could enlighten us! BTW, what do I need on my computer to open a .dxf file? Autocad? Know a .dxf file can be imported into MasterCam.

AutoCAD will open dxf's, but you can use this to open it:

http://www.solidworks.com/pages/prod...gs/viewer.html

[Crashmaster]

But I must ask the question.... Any advise on this part. It is driving me and my boss crazy. HELP A NEWBIE IN NEED!!!!!

[g-codeguy]

Originally Posted by rustamd AutoCAD will open dxf's, but you can use this to open it: http://www.solidworks.com/pages/prod...gs/viewer.html

Thanks for the link. It did the job!

Crashmaster: I hope someone comes along soon to give us a lesson on knurling.

[Geof]

Originally Posted by g-codeguy .....Picked up a used Hardinge not long ago that came with a knurling tool I hadn't seen before. Looks like you cut with the edge of the tool, and feed in from Z-axis. I know that pitch and diameter are tied together, but that knowledge doesn't seem to help me much....

I have not knurled on a CNC but in the past have done plenty on Turret and Center lathes.

To comment on your second point yes there is a relationship between the knurl spacing and the diameter; you can consider the knurl and the workpiece to be a pair of gears so you have to fit an integral number of bumps around the workpiece. But at the same time your workpiece is changing diameter because the bumps come up as the hollows go down. I suppose it would be possible to calculate a 'pitch diameter' for the knurling and make that your starting diameter; I nearly always did it by trial and error.

Regarding feeding in from Z that is how we did it on turrets, both straight and diamond knurl; it wasn't really feasible to do anything else. It also seemed to be easier and I always figured it was because the knurl was working on a smaller area of metal. If you come in on X the knurl touches across the entire face and is distorting the workpiece simultaneously on the full width of the knurl; coming in from Z means it is plowing through into the workpiece only on the leading edge.

On a center lathe I would come in at the end of the workpiece with the cross slide and have the knurl overlapping just a small amount. This would start the knurl and get everything in synch and then I would traverse along with the carriage.

Sometimes I found the knurl would start to cut a double start with the knurl rollers spinning twice as fast as they should be; you could see the different appearance on the work when this happened. I would back out and start again. This would leave a poorly knurled section at the end but generally after knurling I would re-chamfer the start end to remove the sharp burrs that the knurl pushes out on the end.

Incidentally starting from the needs a bit of chamfer before knurling to allow the knurl to ride into the part.

Regarding holding +/-0.001" when knurling I don't see how that is possible. Also if the picture that was posted is the part being done I don't see why it is necessary, the knurl is on the handle of a screw-in alignment pin. It would be a very sensitive hand to detect a couple of thou difference in diameter.

[Crashmaster]

The part is actually an arbor that is pressed inside of a tube. It the knurl is to big, the tube will bend when being pressed. If the knurl is too small it wont stay in the tube.

[Geof]

Originally Posted by Crashmaster The part is actually an arbor that is pressed inside of a tube. It the knurl is to big, the tube will bend when being pressed. If the knurl is too small it wont stay in the tube.

Okay, I take it the knurl is then supposed to be acting as a spline that cuts, or forms, it own mating surface inside the tube as it is pushed in. I wonder if anyone has tested this approach rather than a simple press fit. I doubt that it gives a better load carrying capacity and would not be surprised if it was less.

[MrWild]

Partly trial and error and then making a note of the depth/ start diameter and feed that produced the desired result. Holding to +-.001 may only be possi-ble with a specialized machine that only does the knurling procedure and not with a multi function lathe. Holding a good knurl all the way to the shoulder is also something that needs a specialized machine (IMO) Some jobs are not worth bidding on due to the frustration and near impossible (with the machinery on hand) oprations required.