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burning chips
01-18-2012, 06:59 PM
I have a 10" Logan Lathe and need to replace the carriage worm. It is a 6 TPI and is similiar to an Acme.

The worm is very damaged and may have a single end thread that has a good partial profile. It was not the correct part for this lathe. The old worm was for a larger (12") lathe with a larger lead screw. The 10" has a 3/4 in lead and the slop with the key drive caused the damage. The axis center distance should be the same. Does anyone know what the correct thread should be. Is it an Acme or something else. I calculate the tip to be .056; Pitch .1666; base width .052; and the depth of the tooth at 0.1143

The worm ring gear seems worn but not enough to replace. I made new bearing caps and bushed with oil lite. Made a new worm blank and am ready to make a tool and chase the thread.

Any help would be appreciated. :)

macona
01-18-2012, 08:01 PM
Logan is still around:

http://lathe.com/

rogeroadster
01-18-2012, 09:35 PM
Logan will get a premium for a new one. There is one for a 10" and one for a 12" on ebay right now if you don't want to pay the high prices.

atty
01-19-2012, 01:10 AM
You might give Finegrain a try on PM. He has a Logan and has a thing for gears. Worm might be a problem, but it's worth a try. If he can do it, trust me, it'll look better than anything Logan did, or ever will, turn out.

:)

burning chips
01-19-2012, 10:54 AM
Logan is still around:

http://lathe.com/
Thanks, I will ask but would like to chase the threads myself.

burning chips
01-19-2012, 10:57 AM
You might give Finegrain a try on PM. He has a Logan and has a thing for gears. Worm might be a problem, but it's worth a try. If he can do it, trust me, it'll look better than anything Logan did, or ever will, turn out.

:)
New to this, what or where is PM.

My better half usually has PMS when I want to work on tools.

atty
01-19-2012, 11:00 AM
http://www.practicalmachinist.com/vb/

camdigger
01-19-2012, 11:33 AM
New to this, what or where is PM.

My better half usually has PMS when I want to work on tools.


Well, this is the first time I've ever seen a link between PM and PMS. Hilarious. Brilliant!

Makes me wish I'd made the connection....:D

Toolguy
01-19-2012, 12:03 PM
They have PMS on PM sometimes too...

Duffy
01-19-2012, 02:55 PM
Brace yourself for Scott Logan's quote. The problem is that little drive spline in the worm that is driven by the slot in the lead screw.
I thought about chasing a new worm, but the spline has me baffled, (which isnt really saying much:D !)

burning chips
01-30-2012, 12:26 AM
Logan did not reply to my questions about the worm. I think it should be a Brown and Sharp Worm. I sent him the calculation that I thought it should be. Was only lookin for a "yes" or "no". No answer at all.

I think the key will capture in the bearing caps but am prepared to tig it in through a couple of drilled holes or something like that.

Duffy
01-30-2012, 11:13 AM
I said the key had me baffled and I meant it!
IF I was to try, I think that I would bore the worm blank to finished ID, cut an internal slot, and then silver braze the key into the slot. It would mean that the worm mandrel would have to be slotted for the blank, but at least I would know that the spline would hold.

Carld
01-30-2012, 09:40 PM
Ron is a friend and we are currently working on a solution. My solution to the key was to broach the worm gear and in fact I did that. I cut a test gear and we tried it today and we found that the pitch Ron assumed it was is not correct. Tomorrow I will cut another test thread and see how that fits. The thread is a B&S Acme worm thread. More on that later.

Scott was not helpful at all and exhibited his normal reaction to a request for information by ignoring it. That's ok, I can make what he needs.

Below left is the worm gear that was in his lathe and the one on the right is the one I made. I cut the keyway and a key to his measurements but Ron said it didn't fit properly. The keyway is an odd size and he is measuring it again to be sure we have it right before I cut it again. The bearing caps capture the key in the worm gear so it's not likely to come out but we both agreed it would be best to TIG it on each end. The chance that it could loosen from use and roll in the slot is paramount in my mind and we will keep that from happening.

When we get it done he or I will post a drawing with complete measurements so it can be replicated by anyone that needs one.

http://i82.photobucket.com/albums/j276/yeathatshim/P1280003.jpg