Welding on an old Startrite Motor

I would like to mount a VFD on the side on the motor of my Startrite Mercury pillar drill. The motor has no points to attach onto apart from its own mount which is welded onto the casing. The middle part of the casing is not cast (the ends are alu castings) so I guess mild steel. I have not been able to get the end castings off, so I'm thinking about making a mild steel bracket and spot welding it on with stator/rotor/windings in place.

I have a stick welder and would drill a couple of 3-4mm holes in the bracket and spot weld it onto the motor casing. Is this a feasible approach or do I run the risk of damaging the insulation on the windings?

The windings will be on the inside of the laminated stator, which is probably pressed into the outer casing. So long as you stay away from where the wires go from the junction box to the end of the stator you should be fine.

I actually had to weld up a crack in the casing of the feed motor of my lathe. The cast iron casing had been split when the end bells were pressed into it.

I have done a similar stick weld. On my motor the windings were clear of the outer shell, it go warm, I didn't linger, did a short run, left it for while to cool then a little bit more. I was fixing the mount for small 3 phase motor on my Fobco drill and I was also going to use VFD. John

Jon

Far safer to weld onto the bracket rather than motor case. If you must.

I'm no fan of welding in that sort of situation as it makes life harder if you have to change things. My late mate Andy the Randy reached for the welding gear first on pretty much any job 'cos it was quicker than making bolt on brackets like wot I did. I still say he spent more time cutting off, griding and re-welding than I did drilling and bending.

I'd just make a bracket to share the motor mounting holes.

However if you plan to use the VFD controls on the box rather than make up a remote button pendant putting it on the motor will be way too far back for easy driving.

Given the low motor power the VFD box will be compact so it could easily be mounted on the left side of the machine in front of the rotary switch so the speed display and buttons face you.

I was impressed by a picture of one mounted that way with a lever to operate the rotary switch alongside. Presumably the maker had arranged bearings behind the VFD to capy the lever witha fork, slot or similar to operate the switch. Red ball on the end of the lever so as to be obvious whethre switch was on or off. Presumably ball forward was on, ball up or down off.

Never really cared for the standard switch on the side location as it's slow tor each in an emergency if you don't fit an additional stop button.

Clive

I would roll a couple of brackets to attach to the motor, without welding, and attach to those, if you must do as you are suggesting.

That said, VFDs are generally recommended to be fitted in an enclosure, with adequate cooling/air flow, to protect from dust, etc..

A low voltage pendant control is easily wired to the VFD for remote operation, or the operating panel connection wires can be extended to outside the VFD enclosure.

Thanks for your comments and suggestions. I will post when I get it sorted .... workshop is full of UFO's (Un Finished Objects) that have build up over vinter.

I've welded stuff to motor casings several times never had a problem. I welded ally feet to an ally cased motor with a 200a tig welder and even that didn't cause any problems.

Hi all, I finally got around to this job. In the meantime I thought about using a couple of large hose clips, so went ahead and tried it. It is very solid when the clips are tighten up and just need a plate to mount the VFD on then and bolt onto the bracket. Should it ever come lose it will get 4 tack welds to sort it.

Big hose clips like that do just fine holding up chimney liners and the like so you should be OK.

The big ones are cheap from building supply places and very useful for strapping stuff together when doing the common temporary the becomes permanent job. Handy for welding positioning too 'cos they don't melt like the plastic zip ties.

Couple or four of the big hose clips and a packet of the big, lever release, zip ties are an essentail foundation of any self respecting bodgers workshop.

Clive

I like that solution much better than welding. Looks good and solid and can be adjsuted or changed if need be.

Gasless MIG is far easier for thin jobs

If you do go-for-it get a bit of practice in on a like minded piece of scrap to make sure your timing is spot on

Stick blows through thin material very easily