Can we discuss Dremels?

[Chris Hooper]

I found a Woolworths (Remember them) dremmel clone in the back of the garage when I was prepping for the Westfield. I think dad bought it and never used by the looks of it. It's still holding up but does get properly hot. I bought a diamond cutting disk from Milton Keynes market. I've done the body but not the dash yet.

[Rory's Dad]

I have a Machinemart one too and it's just fine.

[Yanto]

Thank you all for the input, looks like I'm not totally alone in having problems with Dremel.

 

I think I will buy cheap n cheerful and expect a short life rather than more expensive and hope it lasts more than a couple of hours total use.

[Rory's Dad]

Thank you all for the input, looks like I'm not totally alone in having problems with Dremel.

I think I will buy cheap n cheerful and expect a short life rather than more expensive and hope it lasts more than a couple of hours total use.

[Captain Colonial]

Thought after this discussion I'd try to take my Dremel apart and see what ailed it.

 

I got my Model 398 out of the box and also went online to see how others took their Dremels apart.  Turns out to be stupidly simple as it happens, and Dremel actively encourage you to do it and fix it yourself, lots of exploded views and part lists - interesting.

 

So five star drive screws later and it's all apart.  First thing I notice is the two carbon brushes (well, carbon blocks, really) are chipped where it meets the armature - ah good, methinks, this will be cheap to sort.

 

But while I'm in there, I figure I better pull the armature assembly out as well, which is dead easy.  I do so and this is what greets me on one side (click to enlarge):

 

 

Not so bad...until I turn it over.

 

 

Ouch.

 

Obviously the bit that broke off the carbon brush / block decided to go through between the armature and the field coil and make a mess of things (field coil is completely undamaged, strangely).  The bits will cost me about £35 to replace.

 

So there's a tip for you Dremel owners - check your carbon brush sets periodically for wear.

[Yanto]

Pity I threw mine in the bin, never thought about stripping it.  I actually didn't know they were classed as serviceable by Dremmel. 

[Man On The Clapham Omnibus]

Can't see the damage Scott. Has it cut the windings?

[Captain Colonial]

Can't see the damage Scott. Has it cut the windings?

Click on the photos to make them bigger. On the second one, you'll see very deep gouges in the windings.

[Man On The Clapham Omnibus]

Scott, you don't mean the steel coloured centre part do you? That's the laminates and the elliptical gouges are balancing machining. I looked carefully at the copper windings at each end in your second picture and saw nothing.

[Captain Colonial]

Really? Those gouges are supposed to be there? Wow. Thanks, had no idea it would be that crude, I assumed balance weights would be used. It would explain why the inside of the field is undamaged. You may have just saved me £21. I'll just order the carbon brushes now and see what happens. It spins freely and smoothly without the old brushes, so worth a try - thanks again.

[Dave Eastwood (Gadgetman) - Club Chairman]

Indeed, I thought they usually just had a sacrificial block/web somewhere that they drilled material out of to balance it. Not seen an electric motor balanced like that before, but I can't say I've pulled that many apart!

Is that your new catchphrase MOTCO?

[Man On The Clapham Omnibus]

Yes Dave, it's the French Navy motto. Just say it out loud a few times in a cod-French accent and you'll see...

 

Scott, you can test the continuity of the armature with a meter set to resistance. The commutator segments are connected to individual windings so put a probe on diametrically opposing commutator segments and you should get a reading of  (probably) a few hundred Ohms on each. It is highly likely that the brushes are responsible and that the windings are intact. Make sure no adjacent segments have copper 'whiskers' dragged across to short circuit against their neighbouring segments. 

 

I worked at Hoover's in Perivale as a yoof and they balanced armatures for vacuum cleaners in various ways including drilling holes, pressing weights into the laminate, and machining metal off the laminates. It's impossible to wind an armature such that the distribution of the magnet wire (the copper) is evenly distributed vis a vis the rotational mass, so dynamic balancing is imperative for a smooth running motor.

[Dave Eastwood (Gadgetman) - Club Chairman]

Oh I already had Clarence!

[Man On The Clapham Omnibus]

[Dave Eastwood (Gadgetman) - Club Chairman]

Damn there goes my cup of tea! :laugh: