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Overheated Drill

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Adrian R231/08/2021 12:11:00
118 forum posts
5 photos

Tea Room as I'm presuming this is a lost cause! I overheated a handheld power drill last week through impatience with some DIY, causing some smoke and eventually blowing the fuse.

Once it had cooled down I found that it would no longer spin, just hum - dismantling showed some melted and resolidified wax/resin substance had jammed the armature. With this pared away and drill reassembled it turns again under power but only slowly and gets hot again very quickly.

Waxy stuff looks to have come from stator windings; I tested continuity of both halves of this while it was apart and got around 5 - 6 ohms each so not completely burned out but I suspect internally shorted (?)

Can anything else be done/checked apart from learning some mental relaxation techniques?


broken b+d.jpg

Edited By Adrian R2 on 31/08/2021 12:11:42

John Haine31/08/2021 12:30:58
4170 forum posts
242 photos

I suggest you recycle it, not worth the effort and risk of trying to mend it.

Howard Lewis31/08/2021 12:53:19
5298 forum posts
13 photos

Sadly, I fear that at least one of the armature windings has gone open circuit.

Because of this, it runs at low speed, and does not generate enough back EMF to reduce the current draw; hence the slow and hot running.

If you want to investigate, start checking across diametrically opposed commutator bars, you will probably find some that are open circuit..

If you can get a new armature, it may be repairable (Economically or not is another matter )

If the gods smile on you, it is possible that, but unlikely, that it has merely thrown the solder off some of the armature / commutator connections, and a few minutes work with a soldering iron will restore life..


Adrian R231/08/2021 15:28:10
118 forum posts
5 photos

Right, thanks, much as I suspected. I shall put it in the rainy day pile for a bit and then perhaps test the armature.

Job was drilling through about 2ft of rough stone grumpling which kept jamming the bit, even using hammer mode. Would an SDS be a good upgrade for it's replacement?

Rod Renshaw31/08/2021 15:41:28
325 forum posts
2 photos


Derek Lane31/08/2021 15:47:04
524 forum posts
96 photos

The majority of the time if an armature goes then a machine is destined for the scrap pile as they seem to be the most expensive part of any electrical machine.

SDS drill is a better option always buy a replacement that is rated for the size of bit you intend to use don't skimp on this, if you drill say 25mm most of the time then pick a machine that caters for this and the size is in the mid range of the machine therefore you are not drilling at the maximum capacity.

Speedy Builder531/08/2021 15:55:23
2407 forum posts
191 photos

That was a pretty small drill for that application. The cost of drills has fallen dramatically since the 1950's and a serious DIYer would have a smaller variable speed battery drill, a small mains hammer drill for medium work and an SDS hammer / chisel drill for heavy work. Of course you will need some SDS drill bits but many SDS drills come with a "Jacobs" chuck which have an SDS male fitting.


Adrian R231/08/2021 16:22:53
118 forum posts
5 photos

Grumplings are stone footings at the base of a wall, or they are hereabouts anyway.

I have a bigger Wolf drill, but it's heavier to handle and I thought this one would manage as it had done similar jobs before. Hole was only 15mm dia using an extended masonry bit, but for some reason the drill kept grabbing and stalling out. I should have stopped and changed tool, but I didn't and so here we are.

Fortunately no pressing need for an immediate replacement, but does look like SDS is the way to go if this one can't be rescued.

[Edit: thinking about it the 2ft in my original post was a bit exagerated, probably more like 18". Enough to need the extension bit anyway]

Edited By Adrian R2 on 31/08/2021 16:32:59

John Haine31/08/2021 16:52:24
4170 forum posts
242 photos

Builders I have spoken to don't expect even quite expensive drills to last much more than a year or two.

noel shelley31/08/2021 18:12:31
758 forum posts
19 photos

Keep the chuck and throw the rest away ! Bosch do some good SDS drills that have both an SDS chuck and a Jacobs type. A very useful function is the rotary stop, so just hammer, great for both wood chisels and stone cutting/breaking. Bought one 10 years ago, worth it.s weight in gold. Noel

David Caunt31/08/2021 18:19:35
73 forum posts
20 photos

And you will find that all these drills are fitted with a 13amp fuse which means the the first thing to give up will be the armature. When I repaired them I used to put a fuse which suited the wattage of the drill.

This usually meant the fuse went the user then replaced it with a 13 amp fuse and then the drill ended up with a burnt out armature. That was 40 years ago but I doubt the are fitted with an overload device even now.

Mikelkie31/08/2021 18:23:58
124 forum posts
13 photos
Posted by John Haine on 31/08/2021 16:52:24:

Builders I have spoken to don't expect even quite expensive drills to last much more than a year or two.

Correct. the smaller drills and angle grinders became a consumable item i go through 3 each annually and

bin them, not worth even opening them.

Rod Renshaw31/08/2021 18:29:58
325 forum posts
2 photos

Thanks for the explanation of "grumpling", not come across that before. Good luck with the drill.

not done it yet31/08/2021 22:27:35
6322 forum posts
20 photos

Looks like a half inch chuck, so expecting a lot, especially without a pilot. Likely nowhere for the drillings to go caused the stalling? As we used to say ‘expecting a boy to do a man’s job’.

Not all SDS drills are equal, btw. Couldn’t even get a spare trigger switch for a TitanTTB278, recently.

Emgee31/08/2021 23:20:56
2156 forum posts
265 photos

Drilling deep holes in any kind of masonry requires an drill with unworn tips, otherwise when the hole becomes deeper the less worn drill flutes are bigger in diameter than the front section of the drill, result is the drill stalls in the hole.


Adrian R201/09/2021 09:21:02
118 forum posts
5 photos

Agreed, however in this case the "boy" was over 25 and had done similar sized holes before, even 22mm for plumbing jobs. Drill tip is OK so I'm sticking with my theory of uneven stonework jamming it up.

The point about fuses is very valid, my angle grinder was once saved after a snarl up by its 5A fuse blowing before further harm was done, unfortunately I didn't think to check what was in the drill which was indeed 13A.

Ady101/09/2021 09:35:27
4728 forum posts
714 photos

The last two 240v ones I got from Lidl were 19.99 each, less than 2 packs of smokes

750W-reversible var-speed hammer-option 3 year no-quibble guarantee

An Other01/09/2021 11:05:11
210 forum posts
1 photos

While I agree with the arguments about getting the correct size and type of drill for the job, I have had some experience with a hamfisted neighbour - I had three drills of various sizes, one of which was a Skil drill I had owned for about 10 years - all the drills got extensive use by me, with no problems - then my neighbour borrowed two - one being the Skil.

Later in the day, I saw him using the Skil to drill holes in a brick wall, and obviously making heavy weather of it - bearing down hard on the drill, slowing it to the extent that it almost stopped. I suggested he just back off a bit, and let the drill do the work, but it was a waste of time - an hour later he came and told me it had stopped working. When I picked it up, it was still extremely hot. So clearly technique matters as well. (he never did replace the drills - and doesn't get any of my kit now)!

SillyOldDuffer01/09/2021 11:36:31
7549 forum posts
1680 photos

Posted by An Other on 01/09/2021 11:05:11:


I suggested he just back off a bit, and let the drill do the work...


Letting the tool do the work is perhaps the single most important workshop lesson I had to learn. Not as easy as it seems: hard pressed power tools mince their own swarf, go blunt, wear their brushes and burn out their motors. More haste, less speed! But slowing down too much is just as bad: when a cutting edge rubs it soon goes blunt, causing more havoc. Surprisingly easy to blunt tools by rubbing.

The material makes a big difference too. The sweet-spot between not too fast and not too slow is quite narrow on work-hardening metals. RPM, cutting pressure and edge condition are critical on some types of stainless steel: far more awkward to cut these than leaded mild-steel.

I had to learn to position my technique between namby-pamby wimp and bad-tempered gorilla. By nature I tend to over subtle, but turn quickly into the Incredible Hulk when frustrated. Neither extreme does good work...

I suspect many workshop skills depend on learning the sweet spot and then staying in it consistently. Any other examples come to mind?



Edited By SillyOldDuffer on 01/09/2021 11:38:41

Howard Lewis01/09/2021 11:40:43
5298 forum posts
13 photos

ANO's experience is why I am VERY wary of lending tools to other people.

Either they are not returned, *"No. Never had that" or come back damaged or ruined.

I would rather go and do the job myself.

Amazing how many non engineers seem to think that any spanner will fit any bolt, and that power tools have an infinite reserve of power.

The epic was the person who complained that the drill was not cutting.

It worked better when I rest the drill for normal rotation rather than reverse!


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