Did I Leave Enough Material to Grip for Knurling?

[SteveHGraham]

I made this tonight. It's going to be a knob for a CNC lathe. It's aluminum.

I am wondering if I shot myself in the foot by cutting this to size before knurling the big end. The small end is 1" by 1/2". The big end is 2" by 1/2". Will 1/2" be enough to grip if I'm using a scissor knurling tool?

[Bob D.]

Would help much to center drill the face of the large end so that you can use a center in the tailstock to help support the workpiece. A collet would probably hold better than a chuck and give you a little more working clearance. Fortunately aluminum knurls easily.

Bob

[SteveHGraham]

It looks like the knob is supposed to be drilled all the way through, but the hole is 1/4", so not a lot of support for a center. I guess it will help, though.

[SteveHGraham]

I guess I'm not on top of things. This is a scissor knurl, so if I line it up right, there shouldn't be any net force pushing the knob off axis. I'm only worried about the torque required to turn it in the tool.

[RSG]

I would have been incline to have knurled it first Steve, then parted it off and face it. Since you have finished it though you can probably chuck it up leaving a bit out of the lathe and do it without issue. You might want to protect the surface of the small end in the chuck though from bit marks.

[Harold_V]

Would help much to center drill the face of the large end so that you can use a center in the tailstock to help support the workpiece. A collet would probably hold better than a chuck and give you a little more working clearance. Fortunately aluminum knurls easily.

Bob

A non-issue with a scissor knurl, as the work piece isn't deflected by one-sided pressure.

What would be of concern is if the piece can be held such that the knurling tool can traverse the entire periphery. My personal choice would have been to rough the piece, leaving it attached to the bar, then to turn the knurled diameter to size. I would then have applied the knurl, then taken the other features to size. That way the piece should be concentric and properly machined and deburred. I like to apply a chamfer to the edges after the piece has been knurled.

Harold

[ctwo]

You do not need to worry about twisting off that stub. You might want to try it in several positions for least run-out, for when you champher...

[SteveHGraham]

I really need to think more about order of operations.

[SteveHGraham]

It seems like big aluminum rods aren't all that cylindrical. You chuck them up, and the indicator wanders around pretty badly. Is that just my experience, or are they all like that?

[Harold_V]

Stock isn't generally round or straight (although quite close), even that which may appear to be ground. That can include drill rod, contrary to the opinions of many. For that reason, it is often provided a couple thou oversized (not drill rod, however), so truing cuts can be made without going under the nominal diameter.

If you'd like to have the ability to deal with objects such as the knurled knob you hope to make, you might consider exploring soft jaws. With them, you can grip by the knurl without doing any damage, with the added benefit of being able to do repetitive parts, holding lengths without effort.

As you alluded, before you begin a project, it's wise to investigate procedures, so you don't paint yourself in to a corner.

Harold

[SteveHGraham]

As you alluded, before you begin a project, it's wise to investigate procedures, so you don't paint yourself in to a corner.

Harold

I am now writing from the corner.

The part is now scrap.

1. The section by which I was gripping it was too short. I had to hang it way out in order to provide clearance for the knurling tool to approach the chuck without hitting it, and when I fired the lathe up at 20 RPM, the chuck spun on the part, and that was bad. I am going to have to use 3" of 2" rod in order to make a 2" part. That will give me a 2" handle to grip. Problem: how do I turn the handle down to 1" in length after knurling the fat end? I can't put the fat end in the chuck without ruining the knurling.

2. It looks like it takes a little effort to get the knurls lined up vertically. This is a huge tool (just fits a CA post), and I would say the top knurl was 1/8" closer to the chuck than the bottom knurl. I took the tool apart and tightened everything up, so I am hoping the knurls will line up better on the next try, which will involve scrap.

3. Doing a test turn at light depth is not easy. The nut that adjusts the tightness of the tool is on a threaded rod that projects DOWN from the tool, so you have to get in there with a crescent wrench and play with it. It's hard to see what's happening. I am surprised they didn't make this thing with the nut on top, where it would be easy to work on. I can install the tool with the other end up, but to do that, I have to mount it on the tailstock side of the post, and that puts a lot of metal really close to the chuck, if it's possible at all.

I decided to move the parts around so the nut will project upward. Wondering if there is some obvious reason why the factory doesn't do this.

Time to get out the scrap and see what I can learn.

[ctwo]

I cannot help you on gnarling the part.

But, why not turn the gnarl first, then turn the small diameter close to the chuck, then part off the small diameter right at the jaw? Be sure to face and champher before parting off, or before turning the small diameter...