Knurling Tool

Having purchased some medium knurls some time back (could be as much as 3 years!) and having started to make some machinists clamps I decided it was time to make the knurling tool so I can make knobs for the clamps. This is 'yet another' clamp type design, coagulated from all ones I've seen in print and on the web. I designed around the 12x12 BMS and the 4mm plate on hand.

The adjustment range is theoretically 6 to 40mm though the bit of ali I tested it on is less than 6mm so no problems there. The 40mm end will be tested shortly to make a knob for my spindle crank.

The clamp bolt is deliberately set offcenter to give it some advantage when clamping up, though with my 10mm spanner that is about 6 inches long, clamping it up to depth was almost too easy. Maybe I'll make another 40mm knob for that purpose

For South African readers, I purchased the knurls from Toolquip and Allied. They have a nice web page where you can browse all their products. If you register you can see the prices and place online orders. I have not had any advertising to my email as a result of registering. I have not done an online order since my father in law lives in Port Elizabeth. I find the part numbers on the web and have him pick up the items for me.

The knurls are a bit of a story by themselves. They are stamped 'India' and the cutting surfaces are nicely made, the sides are ground parallel etc etc. However, on making the brass bushes that serve as shafts for them, I found that the holes appear to have been tapped and then roughly drilled out. The result is that they are neither true nor parallel cylinders. They are at least both the same nominal size though. Hence the early test as seen in the fotos below. They run straight enough under load so I'll stick with them for now. They are as hard as can be, so about the only thing I could do is grind them somehow. I don't have a tool for that. Maybe honing will work? The holes are 6.5mm and since they are rough with partial threads, I don't know that a hone will run true. Ah well, they were not expensive and they work ok.


Click on the drawing for a readable size. Right click and choose 'save link as' to save the larger drawing to your computer. Alternately you can download one of the drawing files below. I use TurboCAD5Pro and the TCW is the native format. The DXF file is 'as exported' and I have no remedy if it doesn't work for you. TurboCAD has never been good at DXF files, but that is all there is.

I expect to have to make new brass bushes from time to time. I can handle that. The knurling process creates a lot of fine particles suspended in the lube oil, and this sludge will find it's way into the knurl bearings for sure. I don't think ali and brass will make much difference, but steel will definitely be detrimental to the bearing surfaces. The only other way I can think to do it is to locktite a shaft into each wheel and run that in ball races mounted in the side arms. Sealed ball races should last my sons lifetime but I don't have enough small ones in my scrap box to go this route.

The brass bearing bushes are made just a fraction longer than the knurls are wide. Maybe .25mm wider. Thus the bolts can clamp the side arms to the bushes with just enough clearance for the wheels to turn.

As can be seen in the first few fotos, the side arms were made from prepainted material. This was part of some printing machine. I hacksawed it up into suitable bits, then faced the cut edges in the 4jaw in pairs. They were also faced to length. I have since scraped the paint off and filed chamfers on the edges to make it a bit more finger safe. Subsequent finishing with a wire brush in the drill press made them look nice, but with a few scratches still. The wire brush will smooth sharp edges off, but not remove scratches, so I applied a 3M abrasive wheel to the badly scratched bits for some cosmetic joy. See the 3M wheel on the Tailstock Power Feed page. I'd really like to get a Parkerizing kit to try on some tools. I think that would be nice finish for tooling. Sadly the local gun shop chappy doesn't even know what it is.


knurl/kn000_1083.jpg

I started taking fotos a bit late in this project, thus the first one shows the method of making the cutouts in the side arms. The square plate had been cut for something else, so I just pasted a pattern to it and drilled for the bolts. The pattern was printed on my 24pin dotmatrix printer and used immediately. I have found that using printed templates is ok so long as you: - use it immediately - check the printed dimensions for accuracy. decide what is acceptable for your project. - use good paper - do not use a water based glue

Humidity changes will affect the size of the paper a lot and that is why I use it immediately, and use a spray on contact adhesive. Paper or wood glue makes the paper too wet and stretchy.

Anyhow, set up like this I could center the side arms and bore to 15mm diameter for the clamp nuts.

Last edited February 20 2013 09:53:26.
knurl/kn000_1116.jpg

The second knurl made using the tool, after trial assembly. The first one is on the other end of the bit of 6mm aluminum rod, inside the chuck (it worked so well I had to make another one). Lathe was run at 200 RPM (lowest direct belt speed) and 42 weight hydraulic oil used for lube. Knurls were tightened down with a spanner. I must measure how deep the knurl grooves are so I know how far to turn the clamp. The clamp screw is M6x1 and I suspect the knurls have less than a millimeter of depth. Thus clamping only needs to be about the same as the depth of the grooves. Side feed was by hand for the first one, and under power (my usual fine feed) for the second. Both ways work, but the hand feed was a bit fast, and the fine feed a bit fine. I think 5 or 10 thou per rev would be about right.

Last edited February 20 2013 09:53:27.
knurl/kn000_1127.jpg

Operator side view. You can see I need to slim down or recess the bottom arm screw as it is interferring with mounting the tool in the toolpost. Though it worked like this, and there is little force (save the twisting force as it is fed along) on it, I'd prefer more engagement with the tool slot.

A better solution may be to put that bolt in from the other side, making the hole in the right hand arm tapped. I just made them all the same side as a matter of 'gotta clear the chuck on the other side'.

Last edited February 20 2013 09:53:28.
knurl/kn000_1128.jpg

Gratuitous extra foto from further down the bed. Nicely shows the shape of the clamp nuts. These were made after the scallops in the side arms were made. Turned a bit of 20mm bar down to 15mm with a good finish, cut it off and remounted to cut the other side to 15mm (centered in 4jaw with dial gauge). Faced to length. Hacksawed in half, then marked each side for the holes. Drilled one tap size for M6, the other is M6 clearance. I then used the holes to remount the work pieces to face off the cut edges perpendicular to the holes. This is not so important for the threaded one, but the top one must be nice to take the thrust washer without putting twist forces on the side arms.

The thrust washer is brass (yes I know bronze would be better, but I don't have any), and the lower end of the allthread is polished using a wire brush in the drill press. I find this makes the allthread operate a lot easier under load, with less wear. Of course it should all be oiled for use. Some allthread is very rough where the plating was a bit mucky as it was withdrawn from the tank. Polishing really makes a difference on that surface. This particular bit of allthread was chosen for its smooth surface and polished up even better.

Also, I have not yet found a suitable spring to keep the arms apart. That will make it easier to use but is not essential to the operation of the tool.

Last edited February 20 2013 09:53:29.
knurl/kn000_1143.jpg

All the parts of the knurling tool. Large bolts are grade 8 M5. The smaller ones in the middle are M3 of unknown grade, but they seem to be better than the usual grade 4's I get from the local ironmongers.

I have yet to recess (or slim down) the bolt at bottom right so the horizontal part can fit into the toolpost more securely.

Last edited February 20 2013 09:53:30.
knurl/kn000_1157.jpg

Nearly there. Assembled from the shown parts all I need now is the adjustment knob.

Last edited February 20 2013 09:53:31.
knurl/kn000_11591162.jpg

So, grab your hacksaw and get started, and a mere 18 minutes later you have a 11mm thick slice of 40mm BMS bar.

Yes, a power hacksaw is on the list of projects.

Last edited February 20 2013 09:53:32.
knurl/kn000_1166.jpg

A little bit of turning and facing, and drill and tap M6, mount on a bolt in the chuck and I am ready to knurl the knurling tools knob.

Ready, set, GO

Last edited February 20 2013 09:53:33.
knurl/kn000_1168.jpg

Voila! A lovely knurl on the ~40mm diameter knob. Running at 200 rpm may have been a bit fast for this job, but it worked out. The thing wasn't quite on center due to the 'bolt in the wonky chuck' mounting, but close enough since the tool can move with the job.

Last edited February 20 2013 09:53:34.
knurl/kn000_1173.jpg

The completed tool. I have locknutted the knob onto the shaft for now. I want to use it for a bit and see how well it works like this. If it is good, I'll pin the knob onto the allthread instead, making it a bit neater and shorter.

And I must find or make a spring to hold the arms apart.

Last edited February 20 2013 09:53:34.

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Last modified: February 20 2013 07:52:39.