Re: Servo Motor Shaft Modification

> John Stevenson said "Conversion was very easy".
>
> John. What in the world would have been a difficult conversion? I
> have read this post from you about 10 times in the last couple of
> days. It sounds like you did everything but rewind the motor. And
> how in the world did you do it? When I think about the practical
> problems involved, it seems to me to be one of those things that
> can't be done! You must be a super genius with a team of master
> machinists helping you (well ok I am being a little facetious) but
> holy cow.
>
> 1 When welding up the shaft it must have been glowing red. How did
> you keep the wiring on the armature from burning up.
>
> 2 After welding and adding 1/2 inch shaft length you would not have
> been able to turn the shaft back down by mounting it between
> centers. How did you get the shafts to turn true.
>
> 3 What sort of welding did you use.
>
> 4 Did you make the brush holder adjustable for optimal running in
> forward and reverse?
>
>
> Wally
>
>

First off replies to Wally, then some more general remarks and a reply to Ron.

[1] and [3] This was weld with MiG and the heat genertaed isn't enought to get up the shaft and cause any damage.
[2] The armature was put between centres before any weldng was done and a steady set to run on the 17mm bearing diameter.
The steady was opened up and the shaft welded then put back. This way it has to run true.
[4] The brush holders are diametrically opposed and I can't see how without making a complete new end you can do anything about this.

Now Ron:-
///Heads up on quick cooling after weld. Whatever ya do, don't quench it in water. It will heat treat it to like 65 rockwell and it is impossible to machine.
As you say "Why weld?". There is no point in it. If the shaft is too small just machine a sleeve adapter.
Thats a very common practice. How someone could weld extensively on a motor shaft within close proximity to the
armature and not damage it. And if the weld was quenched and was machinable afterwards is a mystery to me.
The insulation on the conductors is paper thin and if its compromised in the windings the motor would be destroyed.
Not saying it couldn't be done but, I definitely wouldn't try it.
Ron
////

First off I spend a great deal of my working life working on electric motor repairs and building up by welding is a normal day to day job.
You really have to pour some weld / heat into a rotor or armature to cause damage. Remember these thing are baked at 400 degrees.
Welding and quenching will cause hard spots or general harness IF and only IF your are working with alloy steel shafts to start with.
You cannot take a mild steel shaft heat it and quench it to harden it, you need to case harden it to get it harder.
Using mild steel shafts which most cheap small motors use and mild steel MiG wire will not harden.
Mild steel cannot be hardened and tempered - fact.
The insulation as I have stated before can and does handle heat greater than most people expect but MiG doesn't pump the amont of heat
in that arc welding produces.

Now for Why?
There are many different types of treadmill motors. The ones I have use a dished pressed steel end cap and there is 1" of 17mm shaft prodruding
with a 5/8" length of 1/2" UNC LH thread on the end of that.
To fit the Z axis of my Bridgeport the shaft will have to stick thru a 3/4" deep casting and then the 1-1/4" long pulley fits on.
As you can see I have 1/4" max of 17mm to secure the pulley to. To turn the thread down I would be left with about a 3/8" shaft, hardly strong enough.
This way I now have the full 1-1/4" to secure the pulley to after going thru the housing.

I didn't go for an adaptor sleeve as with the total length needed of 2" and having to contend with a course LH thread a sleeve would be very liable to
give problems with side loading.
As I say I do a lot of this type of work daily and it's not that much of an issue.
Here's a shot of a largish DC motor out of a fork truck where the woodruff key has split the shaft, very common with woodruff keys, they should be banned.
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/woodruff1.jpg
Next shot shows it built up with weld, good shot this as you can see the amount of heat that's gone into the job on the bearing diameter next to it, hardly anything.
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/woodruff2.jpg
Last shot shows it remachined and rekeyed but with a normal key which is a lot stronger
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/woodruff3.jpg

John S.







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