Sunday, May 19, 2013

Simulated Dovetail Knurling Tool

One of my blog readers suggested a subject regarding knurling in the lathe. He had watched one of my YouTube video's where I ask viewers to submit their metalworking problems. If I think the problem is of general interest to the community and will make a good presentation I'm all for it.

The first problem I ran into on this request was I don't actually have a knurling tool holder. I have never bothered to buy one because their expensive and don't get used that much. Typically I will put a gripping surface on a knob or handle with a different method, partly because I don't have a knurling tool. Your classic catch 22 self fulfilling prophecy.

What I was able to do to move forward on this project was to borrow a smaller knurling tool holder and make a new quick draw simulated dovetail tool block that fits my large Aloris tool post.
Here is the knurling holder I  was able to borrow. It fits an baby AXA sized tool post and my lathe uses the Conan  arm breaking CXA size. Aloris in their wisdom at least made the knurling head separable from the tool block probably so they can do the same thing I was planning on doing. 
After dissecting the holder you can see how it was attached to the AXA tool block with two cap screws and a pair of locating dowels. Now all I need to do is make a CXA sized block that has the same bolt pattern in it. 
Scrounging around the steel bin I found some likely accomplices for the tool block. The larger round bar is for the height adjustment knob that rides on the stud in your typical Aloris tool holder.
A few months ago I wrote an article about this Skeleton tool holder concept. I made this one to hold my button indicator in the lathe so I didn't take up a valuable tool block to keep an indicator set up all the time. This is when I had the four jaw mounted on the lathe for a long period of time. The rods that interface to the Aloris toolpost are .500 diameter. When spaced correctly with my handy dandy rod spacer they form a facsimile of the dove tail cut in a normal tool block. My reasoning for doing it this way is one, I have some smaller material I can use right now to make a block, and two cutting large dovetails like on a CXA tool block takes a long time. I figure for a tool that I won't use that often it will be just fine.
I had to add some to the front face of the new block so the dowel pins would have some meat around them. Welding was a quick way to widen the face instead of the alternative which was start with a much larger piece and hog off most of it. I didn't have larger piece so this is it.
Here is the block all welded up with the simulated dovetail rods. Time for some knob action.
So here is the catch 22 part. I don't have a knurling tool so I added some circular cutouts to provide a gripping surface to the knob. I suppose I could have waited and knurled the adjustment knob as the first test part. The stock Aloris tool posts use a 7/16 stud of all things. I only had 3/8-16 studs in stock. I like to use long set screws for fixed studs like this. They are easy to bottom out in a tapped hole and get tight with the internal hex drive. The ID of the knob is tapped to fit the stud to provide the height adjustment. Incidentally the knob is 1.38 in diameter. I held it down with a single 10-32 screw in the center to do the fluting. I mention it because most machinists would probably prefer a larger screw. When torqued down a little 10-32 can give over a thousand pounds of clamping force. The fluting cuts were done with a 1/4 inch end mill. 
So here is the finished product. Now I can set up to do the knurling video demonstration. Sometimes its easy to find the long way around. I like to think of it as a nice walk in the woods before you get to your destination.

Thanks for looking.


  1. Tom,

    A big thank you is in order. Your timing could not have been better- I had a blitz of an all-nighter to complete a project before a flight the next morning (which we ended up missing because my fussing with the final touches and assembly). I had ordered replacement knurls which came tuesday, then your video appeared. Everything fell into place: I fired up the lathe, turned the screw I needed, calculated the head diameter like you showed and knurled it with no problem.

    YES! Your tips were key, the project was a success, and I have you to credit with lighting the path.


  2. Hi James,

    Thanks for the nice comment. I'm glad your project came together. Send a couple of pictures of the finished device if you can.

    Kind regards,

    Tom Lipton