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Turning screw threads down

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mariner3302

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#1
I have an 11'' South Bend built in 1937. The spindle thread is 1 5/8 x 8 tpi. Im having no luck finding chuck plates but there are tons of 1 1/2 x 8 tpi. Would turning the 1 1/2 to 1 5/8 work?
 

RJSakowski

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#3
You could rethread the 1 1/2" 8 tpi thread but you would have to be careful to follow the existing thread. You could also just buy an unthreaded back plate.
 

mariner3302

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#4
I've spent the last 3 weeks cleaning, cleaning, disassembling, cleaning, stripping, cleaning, cleaning, cleaning (see the trend?? lol) and now I'm ready to paint. Then it's just putting in the new wicks and reassembly!! I could have saved a week of work if I had just disassembled first and then cleaned but I wasn't sure where I needed to go at first.
 

Technical Ted

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#5
I have an 11'' South Bend built in 1937. The spindle thread is 1 5/8 x 8 tpi. Im having no luck finding chuck plates but there are tons of 1 1/2 x 8 tpi. Would turning the 1 1/2 to 1 5/8 work?
I personally would never consider doing this. As suggested, you can make/thread your own plates. I would only work on my spindles if they were damaged and needed repair.

Ted
 

mariner3302

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#6
That didn't come out right. I meant turning a 1 1/2" threaded chuck plate down to 1 5/8". Not touching the spindle. Basically I want to make a thread protector for the spindle nose to practice and work up to a chuck plate for my 4 jaw.
 

Charles Spencer

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mariner3302

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#8
I am hoping to find something at an auction. So I can turn a 1 1/2" witch seem to be easily found. Much more so than 1 5/8.
 

Technical Ted

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#9
You might be able to get away with "boring out" and re-threading a 1-1/2" backing plate with the same pitch as your spindle as long as there will be enough wall thickness left in the hub when you're done. Two things to consider:

1- You should align your new threads with whatever is left of the old thread.
2- You will need to indicate the backing plate in very well so your chuck will run true after you get it threaded. The inside of the hub also typically has a register area that should fit the spot on your spindle closest to the bearing where it isn't threaded with a close tolerance. Any misalignment will make your chuck run out when mounted to it.
3- For both my lathes I made a male gauge of the spindle. That way, when making new mounting plates I had a way of verifying that the threads I was cutting were deep enough. When making the gauge you can use pitch mikes or I used thread wires to measure the threads. Thread wires are inexpensive and a good tool to have.

When I make a new mounting plate I thread it first, then screw it onto the spindle to finish all other operations and that way I know everything will be perfectly aligned.

Ted
 

mariner3302

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#10
It would probably be better to make one from scratch than modifying one. I read somewhere that cast iron is better than steel for things like backing plates and the like because cast iron absorbs vibration better. Is that true and if so, should I forgo steel in place of cast iron for spindle caps, backing plates, etc? I thought things were cast because of cost mostly.
 

T Bredehoft

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#11
Cast iron has a completely different grain structure than steel. It doesn't transmit vibration so it damps chatter, etc. It works well for backing plates for that reason.
It also lends itself to being cast to shape then machined to finish size, shape, thread, and so on. That's for the high production outfits.
 

mariner3302

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#12
https://www.ebay.com/itm/183170266117?ViewItem=&item=183170266117 Just received the 'Students Shop Reference Handbook'. Going to read through it. I need to get the Machinery's Handbook but can't decide whether to get the latest one or a less expensive version that may not have info on 3d printing, new materials, etc...
 

Charles Spencer

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#13

Technical Ted

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#14
It would probably be better to make one from scratch than modifying one. I read somewhere that cast iron is better than steel for things like backing plates and the like because cast iron absorbs vibration better. Is that true and if so, should I forgo steel in place of cast iron for spindle caps, backing plates, etc? I thought things were cast because of cost mostly.
I agree it's best to make one from scratch. Or, sometimes you can buy a cast iron (CI) blank and just finish the machining on it.

As you and others have said, CI is best. A decent grade of CI is what I would call "dead" material meaning that it doesn't have the stresses in it that some carbon and alloy steels can have. Another plus is that it is a dissimilar metal from your spindle and isn't as likely to gall.

That said, every one I have made has been out of a carbon steel weldment, because that's what I had on hand and it works OK for my use. Haven't had a problem yet, although I do agree that CI is better/best. The ones I made are plenty good enough for my hobby shop. The last one I made was for my SB 15" 8" 3-jaw chuck. I welded it up and put it in for the day in my wood stove and cranked up the fire. I checked it a couple of times and it was beyond cherry red into an orange. I left it in there until the next day so it cooled down as the fire went out. When I took it out I had to remove the scale that had formed on it, which is normal during normalizing, but it machined very nicely and the burnt edges were nice and soft.

I don't know what your experience level is, but if you haven't done any single point threading in your lathe yet you might want to consider making a gauge the same size as your spindle first. It's easier to start on an external thread where you can see things rather than start with an internal one.

Good luck and have fun learning!
Ted
 

mariner3302

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#15
Thanks!! I'm actually really looking forward to this project once I have her back together!
 

12bolts

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#16
I find large threads easier to make than smaller ones because mistakes are easier to spot.
Ive also found that its a lot easier to repair mistakes on larger ones and machine them out. Smaller threads tend to melt and require more filler rod...........
 
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