How should I make this longish screw?

[WobblyHand]

Beginning to see why one would go with multiple pieces. (Dawn rises over Marblehead.) Dang, that's a skinny long piece so far. I turned the 1" down to nearly 1/4" for 52mm. Yes, I do have a live center at the end. Thank goodness. Got a little bit more to go on the diameter. Final DOC's will be small, since the piece seems like it will deflect in a breeze.

This is what I have so far. Threading went much easier than expected. All cuts under 0.005". Actually cut it almost perfectly. Spun a die on it and it barely cut anything. Used the AXA-8. Cut beautifully.

 

[rabler]

Is it too late to redesign the little arm over to the actual dressing cylinder to use a larger hole?

I find going through this to be a fun learning process. You will now have a basis for thinking about deflection, and length to diameter ratios.

 

[WobblyHand]

Is it too late to redesign the little arm over to the actual dressing cylinder to use a larger hole?

I find going through this to be a fun learning process. You will now have a basis for thinking about deflection, and length to diameter ratios.

The shaft between the knob and the 16mm flange? Yes, I was thinking of making that a larger diameter than 1/4". Then the slot in the piece that captures the tool needs to open up. That would make this screw a little less scary. Unfortunately the diameter has been turned down to ~ 16.4 mm already. So maybe I could go with a 10 mm diameter section there. (Could use a 3/8" end mill for the slot, I think. 9.525 mm opening up to 10mm) That would give me 3mm overhang on both sides to capture the slot, which should be ok.

Haven't made any of the other pieces. I thought this screw would be a challenge, so wanted to do it first. So far, it's making me think. That will help me make better design choices in the future.

 

[machPete99]

For a long threaded section you could single point it using a follower rest. Or use that approach to do 90% of it and then finish with a die.

 

[WobblyHand]

Well, slight problem. One that I hadn't anticipated. Since I don't have a "good" knurler on my Grizzly, I turned down some of the stock past the knob to 3/4" so I could transfer the piece to an ER32 collet on my mini-lathe. I made a straddle knurler for my mini, a while ago, so I wanted to use it instead of the bump knurler on the Grizzly. Finished the screw save for the knurling. It was tricky, but came out ok.

Don't quite understand why just yet, but I had the knurls in the part tear out. (In two places.) It seemed like the knurler dug in and stalled the lathe. Never had that happen before. Used plenty of that stinky sulfur based cutting fluid I've always used. Since it was 8:30pm, decided to call it quits. Tomorrow, I'll skim off the knurls and try again. At least the part is still intact, and not bent, which is good.

Besides that, part is pretty close to print, save for the changes from 1/4" to 10mm. The knob diameter isn't critical, so taking off a 1/2 mm or mm doesn't matter. Besides the knurl failure at the end, was a good day making chips. Lot more fun being in the shop than being outside in a blizzard!

 

[woodchucker]

I had the same happen to me .. I believe it's because we over tightened the knurl scissor, and didn't have any place for the swarf to go, so it came back and ripped out the knurl. Mine was very light by comparison... It's what I think I did wrong. Do you think you may have over tightened?

The other thought I had was that my travel was too slow.

 

[WobblyHand]

I had the same happen to me .. I believe it's because we over tightened the knurl scissor, and didn't have any place for the swarf to go, so it came back and ripped out the knurl. Mine was very light by comparison... It's what I think I did wrong. Do you think you may have over tightened?

The other thought I had was that my travel was too slow.

Probably over-tightening and slow travel. Tightening is weird. Too tight is no good - see exhibit A above. Too loose = bad tracking and a bad knurl. Has to be just right. I'll be less aggressive on tightening it tomorrow. Probably will hand feed as well. Think one gets a better feel for the knurl that way. Had a slow power feed for the bad knurl. On a mini-lathe there is a pretty quick feed. I had bought a gear set to slow it down for a better finish. Apparently not that good for knurling. Oops.

 

[woodchucker]

Probably over-tightening and slow travel. Tightening is weird. Too tight is no good - see exhibit A above. Too loose = bad tracking and a bad knurl. Has to be just right. I'll be less aggressive on tightening it tomorrow. Probably will hand feed as well. Think one gets a better feel for the knurl that way. Had a slow power feed for the bad knurl. On a mini-lathe there is a pretty quick feed. I had bought a gear set to slow it down for a better finish. Apparently not that good for knurling. Oops.

I used to knurl more often. I started out pretty good when I got my lathe, then got worse, then better..Haven't had to do much lately so screwed mine up a bit. I also should have knurled the whole thing then cleaned up where I didn't want knurl.. rather than trying to stop and start. Oh well, it's in the Won't do that again category for me, of course unless I forget what I did...

 

[WobblyHand]

This time, got the knurling to be ok. Not perfect, but a lot better! First erased evidence of the crime by turning it down. Then set up for knurling again. Found the wheels were clogged and jammed with swarf. Removed the pins, cleaned everything up and the wheels rotated smoothly again. Liberal quantities of oil on the wheels, and loads of that stinky cutting oil on the workpiece. Slowed the lathe down, applied knurling pressure until it seemed like it was tracking and hand fed the carriage once down and back. Much better. Added a couple of rings for some visual interest and voila, the knurling was done. Because I could, I transferred the rod to the bigger lathe and parted the piece. Then using some brass shims, grabbed the knurl and faced off the end of the knob.



Came out ok, I think.

 

[rabler]

Looks nice to me!