- Joined
- Dec 18, 2019
- Messages
- 7,390
Just learned the trick of making acme threads, so thought I'd make an adapter for a broom handle. Broom handles are threaded with an odd thread. It's kind of an acme thread, but not quite. Think it is a stub acme, at least that is what it looks like since the thread depth is roughly half the depth of a real acme. Anyways, all the metal adapters I have seen do not have full depth of thread. I have a push broom head with what appears to be a 3/4-5 acme thread. The wooden handle's threads stripped out, probably because it is a cheap softwood rather than a hardwood. I thought I would design an adapter with a socket for the wood handle and a pin. The threads would be single pointed from aluminum. I was hoping to find some 1.25" 303, but didn't find anything. So aluminum it is. So here's the design I made in FreeCAD. FYI, there are no acme thread forms in FreeCAD, so I had to use a subtractive helix to cut the threads. The nose width of the tool is 0.3707 * P(pitch) which is 0.3707*0.2. As you know an acme thread uses a 29 degree flat nosed form.
I designed a 5mm through hole on one side and a tapped M5 on the other. So I will use an M5 screw to retain the 7/8" broomstick in the socket.
After a little fooling around on the lathe I came up with this:
As you can clearly see, when the thread is just completed, I will be a moment from a crash, at least with this threading tool. I just don't have the reflexes to stop that fast. (Not at my minimum speed of 100 RPM. 5 TPI is fast at 100 RPM!) So I will regrind a new tool that has some asymmetry, so I buy myself a wee bit more time. Or I conjure up a way to reverse thread this. I'll be ok with hogging it out with a 60 degree form first to remove the bulk of the material, or at least I think I can pull that off. If I figure out how to do thread to a stop on my ELS, I won't have to worry about stuff like this. But I haven't figured it out...
I'll grind the tool from some 1/2" HSS, only because it is longer than my 3/8" HSS material. In an AXA I only get 3 screws of contact on the HSS using 3/8" HSS. To avoid the lead angle problem, of a 5 TPI thread, I will grind the tool with 15 degrees of relief on both sides and the nose. Since the lead angle is 5.594 degrees, I'll have about 9.4 degrees on the worst side, which is good enough. It worked for my test piece (1" 5 TPI thread)
That thread gutter was 0.3" wide. The new one is only 0.2" wide and next to a scary shoulder! Well, have to see how much I can bias the cutting tip towards the head stock. (Or come up with a plan B.)
Previously to this I had cut a poor acme thread in steel, I had issues with the crest and valley widths. But I did use the piece to check that a full depth acme would fit in the push broom head. Now I know I can buy a broom stick with metal threads. I have one. But I want to make this piece. Oh, here's a drawing of the broomstick holder.
I designed a 5mm through hole on one side and a tapped M5 on the other. So I will use an M5 screw to retain the 7/8" broomstick in the socket.
After a little fooling around on the lathe I came up with this:
As you can clearly see, when the thread is just completed, I will be a moment from a crash, at least with this threading tool. I just don't have the reflexes to stop that fast. (Not at my minimum speed of 100 RPM. 5 TPI is fast at 100 RPM!) So I will regrind a new tool that has some asymmetry, so I buy myself a wee bit more time. Or I conjure up a way to reverse thread this. I'll be ok with hogging it out with a 60 degree form first to remove the bulk of the material, or at least I think I can pull that off. If I figure out how to do thread to a stop on my ELS, I won't have to worry about stuff like this. But I haven't figured it out...
I'll grind the tool from some 1/2" HSS, only because it is longer than my 3/8" HSS material. In an AXA I only get 3 screws of contact on the HSS using 3/8" HSS. To avoid the lead angle problem, of a 5 TPI thread, I will grind the tool with 15 degrees of relief on both sides and the nose. Since the lead angle is 5.594 degrees, I'll have about 9.4 degrees on the worst side, which is good enough. It worked for my test piece (1" 5 TPI thread)
That thread gutter was 0.3" wide. The new one is only 0.2" wide and next to a scary shoulder! Well, have to see how much I can bias the cutting tip towards the head stock. (Or come up with a plan B.)
Previously to this I had cut a poor acme thread in steel, I had issues with the crest and valley widths. But I did use the piece to check that a full depth acme would fit in the push broom head. Now I know I can buy a broom stick with metal threads. I have one. But I want to make this piece. Oh, here's a drawing of the broomstick holder.
