10" Utilathe Thread dial and worm gear

[darrin1200]

Good morning.

I haven't been a super active member, but I picked up a Standard Modern 10" Utilathe last fall. I have not worked with a metal lathe in a lot of years, so complete newby is how I would describe myself.

I have been doing just basic straight cuts, mostly in wood, plastics and ebonite. I finally decided to give thread cutting a try, with disastrous results.

I set everything up to do a 1/2"-20 course thread. I am making a spare toolrest post for my woodlathe. I set the lathe speed to 75, the ABC-shifter to C, and the tumbler in the 3rd hole. Everything I have read, including the very thin manual I have, says that I should be able to engage the half-nut on any graduation of the threading dial. I tried this, and the threads were trashed on about the 3rd pass.


I made multiple attempts at this thread, each time on the 2nd-4th pass, the threads would be destroyed. I started to pay attention to where I engaged the half nut. I also tried only on numbered graduations as well as only on even numbered graduations. No luck. The only thing I haven't tried yet, is engaging the lead screw on the exact same graduation each time.

I finally started looking into the worm gear and lead screw. The guy I bought the lathe from said that he had replaced the worm gear with one made out of Delerin. I have the original chewed up gear, as well as a spare delerin gear. He also gave me a cutter that he used to cut the teeth into the worm gear.
This is what he gave me. The original gear is in the fixture on the right. The other downside, is I'm not sure how to use this fixture to make a new gear.

I counted the teeth on the Delerin worm gear, and there are 34T, The original is supposed to be 32T. I checked the cutter that he gave me, and it appears to mesh perfectly on the lead screw.



With my complete lack of experience, I am not sure what to do. I tried keeping the half-nut engaged, but there is not brake on this lathe. So out of three tries, I had three fails. getting the lathe to coast to a stop where I need it, is tedious and is going to take a lot of practice to do it consistently. The threads that I eventually need to be able to make, are very fine multi start threads, such as in a pen cap.

Any advice, thoughts or suggestions, would be greatly appreciated.

Darrin

 

[Bob Korves]

Check to see if the correct change gears are mounted between spindle and the quick change gear box. Also make sure the threading dial engages on exactly the same spot for each pass. A little off (one tooth) can ruin the job. Here is a tutorial for threading while using a threading dial:

 

[DAT510]

Hi Darrin,

I’ve been looking at what you described along with your pictures and comparing to a copy of a manual I found online. Granted it’s for a 12x30, from the pictures it looks like their designs are similar.

http://www.standardmodernlathes.com/docs/manuals/standard-modern-utilathe-1230-inch-manual.pdf

Please correct me if I’m misunderstanding.

1) From your pictures and comparing to the manual (items # 39, 41, 42), it looks like you are saying the previous owner made a new drive gear for the treading dial? And that gear is 34T vs 32T on the original? Are the extra gears he gave you also 34T?

Is that a cutter in the lower left of your 2nd image? If so it looks like the previous owner may have “hobbed” the replacement gears.
Here a video of a super simple Hobbing setup someone posted on Youtube, that will give you some ideas of how he may have done it.

If the in the treading dials is 34T, and the original was 32T, then that would definitely make the Treading Dial unusable. But that shouldn’t prevent you from cutting thread if everything else is working correctly.



Btw, could try calling Standard Modern, they are still in business and may have a replacement treading dial gear available. http://www.standardmodernlathes.com

As Bob mentioned above, make sure the treading gears (15, 16, 17) are setup correctly for Imperial Treading vs Metric.

You mentioned you were having issues trying to stop the lathe in time, by just turning it off, while leaving the half-nut engaged. If you are just testing to see if the threads would be cut correctly, if you left the half-nut engaged, you could do something as simple as replacing the cutter with a sharpie mounted in your tool post, so you don't have to worry about crashing the tool. Then using a longer rod, you could "draw the treads" on the rod. Turning off the power and letting it coast to a stop. Back off the cross feed, and then spin the lathe backwards by hand to the starting point, leaving the half nut engaged the whole time. Then move the cross feed back in until the pen touches the rod, and start the lathe again.

After a couple of passes, while never disengaging the half nut, if the sharpie traces overlap, then it will tell you it's most likely a treading dial issue. If not, it will show you that you need to look further, possibly at the treading gears or other setup issues.

Hope this helped.

 

[Bob Korves]

You can also be conservative when letting the lathe coast to a stop, and if stops with the cutter still in the thread you can turn the lathe by hand to bring it to the end of the cut.

 

[darrin1200]

Thanks @Bob Korves and @DAT510 .

The video link gave me a little better understanding of thread dial. I checked the gears, and they seem to be the correct ones for Imperial. I also experimented using a sharpy (what a great idea) on a long rod. With leaving the half-nut engaged, I was able to continually reset the carriage to the beginning. I also made scratch cuts in the steel rod using three different thread pitch settings. They all measured out correct, confirming that the gears are imperial.

I reinstalled the worm gear and played around using the sharpy and the thread dial. It confirmed what I thought, this gear makes the thread dial unusable. I even tried engaging on the same exact spot each time, but the spot that would align, changed each full rotation of the thread dial.

That is a cutter at the bottom of the second picture. I tried hobbing a new gear in white delrin, but there is a lot more to it than I thought. The first attempt, I ended up putting in 36 teeth that were so thin they were useless. The second attempt, was even worse. I have watched a couple of videos, including the one linked above, but I think I am still missing something. Time to set it aside for a couple of days.

@DAT510 , I have 2 manuals, one is for my lathe "10 inch Untilathe" and the other is a military manual for a "Series 2000 model 11 inch". The Series 2000 is almost identical. What I did notice, is that the gears in the "End Gear Train" seem to be very different, including a way to switch between Imperial and Metric. I wish mine had that. Both manuals I have are poor copies of poor copies, so the pictures aren't very good at all. I wish there was a more in depth book for it, all that is included in these manuals, is basic operation and threading info, related to the thread dial. ie when to use which graduation.

 

[DAT510]

To hob a new gear, the Base Diameter is what will determine the number teeth. To get 36 teeth, it sounds like your gear blank was a bit too large in diameter. Is the original gear intact enough to get a Diameter measurement? You could them turn the "gear blank" down the the correct diameter, then hob the teeth.

By the way, here the link to all the manuals Standard Modern has available on their site. They are decent quality. They don't list a 10" but do have an 9" and 11" Utilathe manuals listed.

http://www.standardmodernlathes.com/resources.html

 

[darrin1200]

@DAT510
Thanks for the link. I have been there before, but didn't look at the manual for the 1230 Utilathe until today. It looks like it is exactly the same as the manual I have except for the cover page, and couple of items in the spec sheet. It seems that there are two models in this book, a 10X20 (mine) and a 12X30. The one you pointed to has much better pictures as well.

The only difference between this one and mine, is that I don't have an 8TPI threaded spindle nose, I have a D1-3 mount. But I think this might have been added on later. The US military manual I have for the "Series 2000 11 inch Utilathe" looks exactly like mine on the outside, but has the add on gears for metric, as well as the D1-3 mount on the headstock. I think someone may have upgraded my lathe.

I still have the original gear, but it is missing more than a half dozen teeth. I think my problem with hobbing the new gear, is how I am setting it up and starting it.
I double checked the diameter of my blank, and it is the same as the original. I put the original in the holder on the compound, and it meshes perfectly with the cutter.

I recounted the teeth on my second attempt, and there are 38 very rough teeth cut into it.
My problem might also be the material I'm using. The white delrin I have is very soft, it almost seems to push some of the material aside rather than cut it. I am thinking that this could be why it is not self-feeding correctly, giving me to many teeth. I would try to make a gear out of brass, but I am not sure how hard the cutter is. I believe its homemade, but I'm not sure if he hardened it. I have some harder pieces of acrylic, do you think I might have better luck tying one of them?

 

[DAT510]

You could do a file test on the cutter. Using the corner/edge of a file, try to see if the file will cut (on a non-essential part of the hobbing cutter). If the file cuts, it not likely hardened. If it "slides" across the hob or leaves more of a polish mark, then most likely the hob is hardened. That's a fairly crude test. They also make File Hardness Testing Sets, with different files to determine hardness level/ranges.

If the hob is made from even Mild Steel and you are cutting a soft brass, it should ...... be ok. Mild Steel has a Brinell Hardness of ~130, where soft Brass is ~60-80. I just make sure you are using a lot of lubrication and go slowly. Heat is the enemy.

 

[darrin1200]

Thanks
I did a quick file test, and it definitely is not hardened.
I have some acrylic that I think might machine better than the delrin.
Is there anything special I need to do when setting it up?
How critical is it that the cutter be "exactly" center to the gear?
How do get it to start cutting, before it starts to self feed?

 

[DAT510]

Darrin,

Did you ever get your gear figured out?