07-28-2001, 06:23 PM
southbend wants $374.00 for a thread dial for my 16 inch lathe.I'm going to machine one myself if someone would be kind enough to tell me how to establish what type and size gear i would need.thanks Art.
07-29-2001, 05:25 AM
I can't remember the pitch of leadscrew on 16" SB used to run one 15 years ago. 6tpi I think, maybe it was a 4.
Any how, you need to cover 2 inches of travel with the dial to cut 1/2 threads. With a 4 pitch thread that is 8 teeth, not enough, with a 6 it is 12 and you could get by.
Most dials cover 4 inches, made one for my Logan that only covers 2 but it has a 8tpi leadscrew, so I had 16 teeth so it worked, also I figured I wouldn't ever have to cut a 1/4 pitch thread, isnt on gearbox anyway.
Gear is an oddball, made my own, they are a worm gear but a leadscrew is in Threads Per Inch, worm gears in power transmission are cut to a diametrical pitch.
So if you were making blank for gear, you need to multiply # of teeth by pitch, and divide by 3.1416 which will give you the pitch diameter of gear, then add .5 x pitch to get major diameter of blank. You can make it straight across, ain't a power transmission gear, it is just along for the ride.
Next you need to determine the helix angle of the leadscrew.
Now make cutter, I welded a chunk of tools steel to a shaft and ground like a acme threading tool, the swept diameter just a bit over the diameter of the screw.
Mounted blank in index head, Bridgeport head tilted to helix, found centerline and center of face, and plunged all teeth to depth. I then moved cutter up pitch distance and plunged all again to same setting, then moved up one more pitch distance and did again. I repeated this below center also.
Wound up with a gear that was approxamately proper form, three flats, not a nice proper generated curve, but gear is brass, set loose, and it is just along for the ride, someday I will be worn in to proper shape. i don't think it is hurting leadscrew a bit.
Put marks on dial every 1/2 inch with numbered marks every 1 inch of travel.
PS check with Meridian equipment, he might have one
There was an article in Home Shop Machinist (or was it Projects in Metal? Joe, you ought to publish *ONE* magazine!) a few years ago about making a threading dial for a SB. The article suggested buying just the gear from SB and making the rest.
Halfnut's idea of making the gear is perfectly feasible though. There is no load on it to speak of, so it doesn't have to be perfection. Ivan Law's book "Gears and Gear Cutting" might give you some encouragement if the idea seems a bit daunting. It really isn't all that difficult.
Oh yeah -- I also second Halfnut's idea of checking with Meridian; also Plaza Machinery and Dave Sobel. I expect even a used one won't be cheap, but it will be a whole lot less than SB's price.
[This message has been edited by SGW (edited 07-29-2001).]
07-29-2001, 05:47 PM
Thanks halfnut and SGW for your help.I think I will contact meridian and sb for the gear and then go from there.art