Dumore D3 dental lathe restoration project

[gophert]

But it should be like this one

Stop sanding stuff down to bare metal!

Next time, try using some Mother's Polishing compound (#9 swirl remover) to brighten up the tag you started with. It would have turned the black paint to gloss without removing much if any paint - just enough to make it glossy.

Now you can try some thinned out black enamel (like a bottle of testers model paint or you can also spray some black into a cup.
Then apply over the whole tag. Then immediately wipe it all off with a little silk screen squeegee. They should be 2 to 6 dollars at a hobby store. Or you can try a Bondo applicator from an auto-body store. Or, if you want to risk life and limb, you can use a silicone spatula to wipe the paint off. It must be the stiffer kind so it doesn't sag at the low spots. Don't use too much pressure. Just use light pressure many times to remove the paint.

 

[skysoldier]

Stop sanding stuff down to bare metal!

Next time, try using some Mother's Polishing compound (#9 swirl remover) to brighten up the tag you started with. It would have turned the black paint to gloss without removing much if any paint - just enough to make it glossy.

Now you can try some thinned out black enamel (like a bottle of testers model paint or you can also spray some black into a cup.
Then apply over the whole tag. Then immediately wipe it all off with a little silk screen squeegee. They should be 2 to 6 dollars at a hobby store. Or you can try a Bondo applicator from an auto-body store. Or, if you want to risk life and limb, you can use a silicone spatula to wipe the paint off. It must be the stiffer kind so it doesn't sag at the low spots. Don't use too much pressure. Just use light pressure many times to remove the paint.

Actually believe it or not I did not sand it down at all! I put it inside the bucket with the other parts with Evapo-rust to remove the rust and after a few hours the paint was gone as well as the rust! I will try to repaint it and do as you advice! more to come lol

 

[gophert]

Actually believe it or not I did not sand it down at all! I put it inside the bucket with the other parts with Evapo-rust to remove the rust and after a few hours the paint was gone as well as the rust! I will try to repaint it and do as you advice! more to come lol

Ok, don't do that either next time.

And above, where I said you can risk life and limb by using a silicone spatula - the risk comes in when your wife slaps you silly with the silicone spatula for getting it full of paint.

 

[skysoldier]

Ok, don't do that either next time.

And above, where I said you can risk life and limb by using a silicone spatula - the risk comes in when your wife slaps you silly with the silicone spatula for getting it full of paint.

Ok, no more evapo-rust for tags lol ! Wife? Don't have one so I can have hobbies freely lol

 

[gophert]

Here, before and after on a motor plate from a 1950's appliance motor using Maguiar's buffing compound.

30 seconds of work...

 

[skysoldier]

Here, before and after on a motor plate from a 1950's appliance motor using Maguiar's buffing compound.

30 seconds of work...

sweet! lesson learned! next time I will not put it inside Evapo-rust

 

[rjenkinsgb]

When you rewind the field coil(s), you need to make a simple former from some bits of wood, to get it/them exactly the same overall size and shape as the original, to fits properly around the stator pole pieces. Avoid sharp edges and/or line it with PVC insulating tape to make sure the wire insulation is not scratched.

The enamelled copper wire just needs winding on the former, with the same number of turns (and wire gauge) as the original.
(The modern stuff is typically insulated with polyurethane, but it's still sold as enamelled or "magnet wire").

Put some bits of string across the former slot first and tape the ends to the wood so they do not get lost or in the way. When the coil has the correct number of turns you can release the string ends and tie around the coil so it's held in the exact shape and does not fly apart when you dismantle the coil former...

Then tape it, removing the string ties as you go - ideally with heatproof tape, not PVC insulating tape..

You could soak it in polyurethane varnish before taping, while it's still tied in shape.

You could also use plain cotton tape and saturate that in varnish as you apply it, so it sets in as part of the overall coil.


A common motor winding tape used to be called "Empire tape", which is not made now, though it's still a well known name - this is an equivalent:
https://www.ppmindustries.co.uk/coil-winding-tape-4b

We buy a similar stuff from a local rewinder, plus some thin card-like nomex based flexible insulation sheet for high voltage stuff.
That's also used to prevent wire insulation coming in direct contact with metal components, where it could chafe and short due to vibration.

Varnish impregnated cotton is fine, though, for what you need; it's just which you prefer.


Edit - you should really attach flying leads to the coil before final taping and varnishing. Carefully scrape or sand off the insulation from about a centimetre or so of wire, tin the bare ends and solder on a length of stranded, insulated wire.
Use heatshrink sleeving to insulate the soldered joints.

They should be positioned so they are within the final varnish & tape wrap of the coil, so only the flexible leads are exposed.

Doing that avoids any possibility of the coil ends breaking while you are working on it or later due to vibration; it only takes a few bends in the same are to crack the single-strand wire in the coil.

That type of wire is normally classed as having "solder though" insulation - but carefully scraping it to expose copper first is a lot less messy and smelly.. Any remaining tiny traces of insulation should melt away as it is tinned.

 

[skysoldier]

When you rewind the field coil(s), you need to make a simple former from some bits of wood, to get it/them exactly the same overall size and shape as the original, to fits properly around the stator pole pieces. Avoid sharp edges and/or line it with PVC insulating tape to make sure the wire insulation is not scratched.

The enamelled copper wire just needs winding on the former, with the same number of turns (and wire gauge) as the original.
(The modern stuff is typically insulated with polyurethane, but it's still sold as enamelled or "magnet wire").

Put some bits of string across the former slot first and tape the ends to the wood so they do not get lost or in the way. When the coil has the correct number of turns you can release the string ends and tie around the coil so it's held in the exact shape and does not fly apart when you dismantle the coil former...

Then tape it, removing the string ties as you go - ideally with heatproof tape, not PVC insulating tape..

You could soak it in polyurethane varnish before taping, while it's still tied in shape.

You could also use plain cotton tape and saturate that in varnish as you apply it, so it sets in as part of the overall coil.


A common motor winding tape used to be called "Empire tape", which is not made now, though it's still a well known name - this is an equivalent:
https://www.ppmindustries.co.uk/coil-winding-tape-4b

We buy a similar stuff from a local rewinder, plus some thin card-like nomex based flexible insulation sheet for high voltage stuff.
That's also used to prevent wire insulation coming in direct contact with metal components, where it could chafe and short due to vibration.

Varnish impregnated cotton is fine, though, for what you need; it's just which you prefer.


Edit - you should really attach flying leads to the coil before final taping and varnishing. Carefully scrape or sand off the insulation from about a centimetre or so of wire, tin the bare ends and solder on a length of stranded, insulated wire.
Use heatshrink sleeving to insulate the soldered joints.

They should be positioned so they are within the final varnish & tape wrap of the coil, so only the flexible leads are exposed.

Doing that avoids any possibility of the coil ends breaking while you are working on it or later due to vibration; it only takes a few bends in the same are to crack the single-strand wire in the coil.

That type of wire is normally classed as having "solder though" insulation - but carefully scraping it to expose copper first is a lot less messy and smelly.. Any remaining tiny traces of insulation should melt away as it is tinned.

would this tape work?

Scapa 175/WI160 175 Cloth Tape: 1" x 60 yd, White: Masking Tape: Amazon.com: Industrial & Scientific

Scapa 175/WI160 175 Cloth Tape: 1" x 60 yd, White: Masking Tape: Amazon.com: Industrial & Scientific

www.amazon.com

 

[rjenkinsgb]

That may be OK. The normal cotton tape used for coil windings was not self-adhesive but that looks like a possibility.

Just saturate it in polyurethane varnish after wrapping the coil to permanently hold it in place.

 

[shortbus=]

Can't remember and don't want to go back and read from beginning. Why are you going to rewind? Is it just because of the cotton covered wire?

Unless you have rewound a motor before you may just be making a pretty looking paper weight out of this. If it works, there is no reason to rewind just to get modern magnet wire in it. You are opening up a can of worms that you might not be able to re-close.

 

[gophert]

The last time I attempted to rewind a burnt out motor, I took photos, unwound it a bit, took photos, unwound some more, took photos, repeated. Bought a roll of wire, made a few turns, then bought a new motor.

 

[JimB]

then bought a new motor.

I like it!

JimB

 

[Musicmanager]

The last time I attempted to rewind a burnt out motor, I took photos, unwound it a bit, took photos, unwound some more, took photos, repeated. Bought a roll of wire, made a few turns, then bought a new motor.

Not the easiest project to complete, but not impossible .. .. .. .. .even for a novice like me !

Rewinding a Small AC Motor

Hi Guys I've recently acquired a modellers table circular saw that would be great for cutting PCB blanks. I paid next to nothing for it so I wasn't surprised when it didn't run. A close internal inspection revealed a small circuit board which had suffered some serious 'tampering' and careless...

www.electro-tech-online.com

S

 

[skysoldier]

I am replacing the wire because one the wire is 60 plus years old, and two ( most important reason) wires where literally falling-apart in my hands. I only got it for like 15$ so it is a project, I want to restore it and modernize it to where it is safe to use.
My goal is also to learn form the experience

 

[gophert]

My goal is also to learn form the experience.

That is guaranteed! Whether it is leaning how to rewind a motor, how to cut your losses and know when to quit, or learning that you should have quit sooner next time, or learning to add the price of professional rewinding to the $15 price tag, or learning that an 85-year-old piece of industrial design makes a better paperweight than a lathe.

Remember that the ball bearings or brass bushings (and the grease packed there-in) is also 85-years old like the wire. You can say, yeah, but it hasn't been used in the past 50-years so it is essentially only 35-years old. He technology of grease 85-years ago has come as far as the insulation options on the wires.

Don't stop now, plough through and come to the logical end that you come to. Good luck.

 

[gophert]

The last time I attempted to rewind a burnt out motor, I took photos, unwound it a bit, took photos, unwound some more, took photos, repeated. Bought a roll of wire, made a few turns, then bought a new motor.

Ha, I just mentioned my motor rewinding experience to my wife. She said, I know. Apparently she sent a huge stack of photos from my parent's house off to be scanned. She said the photos of unwinding an electric motor were in there somewhere - she spotted them when she was randomly spot checking them. We cannot find them now.

Thanks to eBay, here is the motor from an erector set (line drawing). The order form (remember mail-order?) is also available from a listing photo on eBay. Wow.

I hope the OP has more patience than the younger me. I think my little brother still has his erector set.

 

[skysoldier]

I was actually thinking of putting bearings instead of the oil bushing but I don't know what size would fit in the shell. I could be a challenge. The grease I can replace ( even if I think they worked with some type of lubricating oil) but the bushing will see if I can find something suitable.

 

[gophert]

I was actually thinking of putting bearings instead of the oil bushing but I don't know what size would fit in the shell. I could be a challenge. The grease I can replace ( even if I think they worked with some type of lubricating oil) but the bushing will see if I can find something suitable.

I had a motor from that era and the bronze bushings were much thinner than bearing races so a retrofit would not have worked in that one. Also, that was the early days of powdered metallurgy and oil was impregnated into the powdered bronze parts with a vacuum process. Frictional heat draws out the oil. It is very difficult to "change the oil" in a sintered metal bushing.

https://www.lm-tarbell.com/history_of_oil_impregnated_bronze.htm

Before self-lubricating, there were little oil pots by each bushing that wept into the gap of the shaft. The pots had to be filled on a regular basis. I had a very early Craftsman Metal lathe that had such oil pots and brass bushings. Correction, a piece of crap Craftsman lathe.

 

[shortbus=]

I am replacing the wire because one the wire is 60 plus years old, and two ( most important reason) wires where literally falling-apart in my hands.

Those had to be the wires going to and from the brushes. Those I would replace with more modern stuff, but rewinding the whole motor? The coil windings are usually varnish impregnated and not exposed to all of the stuff that makes the connecting wires prone to being a problem. But you do what you feel is right.

 

[skysoldier]

Ehm... dumb question... how do I know when I rewire the lathe what cable would be negative and which positive so I can attach them properly and use the right cable color?