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Phosphor bronze half nut

Myford drummond

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Grant Allen 116/04/2019 19:28:10
48 forum posts
5 photos

Is there anyone on the forum, web etc that is able to machine half nuts for the myford m type 3 1/2 ?.

David George 116/04/2019 20:50:31
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752 forum posts
261 photos

Hi Grant You would make it as a whole nut screw cut and cut in half before soldering on to original lever. You just screw cut with a boring bar with a tool with a slightly thinner than original pitch size and widen to suit shaft size with compound slide when to depth. Here is a picture of a new nut I recently made for a wrench that needed replacing.

20190413_160655.jpg

20190413_160703.jpg

David

Hopper16/04/2019 23:09:41
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3495 forum posts
68 photos

Phosphor bronze will wear the leadscrew . Better to use leaded bronnze ie gun metal. I used brass for mine. Did it on the m-type with what was left of the old halfnut in place.

Usual procedure is to tur.n up a bobbin shaped cylinder with small flange each end to take the load. Then take your old halfnut and mount it on the cross slide. Bore out the old threads until the bobbin fits. Then solder it in place. Has been described in MEW several times over the years.

But your halfnut can be incredibly worn before it needs replacing. The threads on mine were worn down to less than .015" thick and still worked perfectly. Bit of backlash does not matter under load.

 

Edited By Hopper on 16/04/2019 23:16:17

Grant Allen 117/04/2019 07:43:49
48 forum posts
5 photos

Do you not need a working half nut to turn thread ? The m type I'm restoring for own use has a few issues one being the half nuts are balder than cojac and I think it's called the back gear you put into drive has 2 missing teeth consecutively. The back gear I thought i could turn off and slot a new on in its place, but haven't researched it properly yet.

Grant Allen 117/04/2019 07:44:44
48 forum posts
5 photos

Would delrin not be a good substitute to make a half nut in?

Hopper17/04/2019 09:20:54
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3495 forum posts
68 photos

You can probably round up a new used backgear off eBay or the Yahoo Group for Drummondlathes.

Delrin half nuts can be made but not very easy to anchor to the odd shaped M-type casting. The brass spool described above can be soft soldered in place.

Yes you need a working lathe to make the new halfnut insert. I was lucky and had the skin of the teeth left on the halfnut, which was enough to make a new insert.

One alternative might be to grease up the leadscrew or cover it with thin plastic wrap then put epoxy repair putty into the clapped out halfnut and squeeze it up against the leadscrew to form it to the thread shape. I would not keep this as a long term fix because swarf could get embedded in the epoxy and wear the leadscrew terribly. But good enough to use to make a new brass insert and then solder that in place.

not done it yet17/04/2019 09:36:20
2802 forum posts
11 photos

One/two broken/damaged tooth/teeth on a gear is/are not too difficult to repair. A complete ring of teeth is an option, but not a necessity. There are several documented ways to repair a broken gear tooth - searching u-toob will provide plenty of ideas - from inserting a pre-made tooth along with a ‘root’ to replacing the tooth with grub screws, followed by filing.

There may not be much more work involved in making a complete new gear in some cases - again, u-toob has plenty of examples.

Edited By not done it yet on 17/04/2019 09:37:16

Grant Allen 117/04/2019 17:56:45
48 forum posts
5 photos

Researching delrin I've found it melts ag 178°, I may look into casting the entire half nut bracket arm etc. I think a few practices are in order first to see exactly how fluid it melts too.

not done it yet17/04/2019 20:29:32
2802 forum posts
11 photos

I don’t think delrin particularly likes to be melted completely and cast. I may be wrong, but the ‘heat and squeeze’ method only takes it to its melting point, not really beyond.

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