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Drill speed controller fault

throbscottle

Well-Known Member
My 20yo Bosch drill has developed a weird fault - it will only start if it's already turning, so you have to give it a twist with your hand before squeezing the trigger. Very inconvenient. Once it's running the speed control still works ok.
So I was wondering if anyone knows a likely cause?
 

MaxHeadRoom78

Well-Known Member
Most Helpful Member
Universal, AC/DC series motor, Assuming it is a corded drill, + on the brushes if it has been well used over the years.
Pays to check the bearings also. ;)
 

throbscottle

Well-Known Member
Brushes were the first thing I checked. I cleaned the commutator whilst I had the case open. Still got a few mm left on them anyway. It's died completely now. 99% sure it's the speed control that's gone.
 

throbscottle

Well-Known Member
I think it didn't like sanding disks...
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Brushes were the first thing I checked. I cleaned the commutator whilst I had the case open. Still got a few mm left on them anyway. It's died completely now. 99% sure it's the speed control that's gone.

Just short the speed controll out, and see if it works then.

However, if it's 20 years old, perhaps time for a new one?.
 

shortbus=

Well-Known Member
Most Helpful Member
However, if it's 20 years old, perhaps time for a new one?.

As someone in the second month of healing a broken wrist from a corded drill, I'm going to finally buy a cordless one. My old Milwaukee Magnum Hole Sooter caught the bit when it broke through the piece of metal i was drilling and twisted my wrist so bad it broke one of my wrist bones!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
As someone in the second month of healing a broken wrist from a corded drill, I'm going to finally buy a cordless one. My old Milwaukee Magnum Hole Sooter caught the bit when it broke through the piece of metal i was drilling and twisted my wrist so bad it broke one of my wrist bones!

Many modern (better) cordless drills are probably powerful enough to do the same - but are VERY expensive, if you want performance approaching that of a decent corded drill. Cheap low power ones are cheap, and low power, the clue is in the description :D

We've got a fairly nice DeWalt small cordless drill (about £100) at work, I use it a LOT, but it's relatively useless if you want to drill holes in walls - far too puny, and hammer is useless for drilling walls. For drilling walls you want an SDS drill.

However, the DeWalt is great for what I mainly use it for (drilling holes in boards, cases, etc.) where my Bosch 850W corded drill would be FAR to big and clumsy - and while it's only an old hammer drill, it's not 'too' bad on walls, but SDS is a LOT better.

An old friend of mine, who used to do aerials/dishesfor us, had (amongst many!) a Bosch 36V cordless SDS drill, and we were on the same job once and I couldn't drill the wall over the fireplace at all (using a cheaper modern mains Bosch hammer drill). He lent me his cordless SDS, and it went in like a hot knife through butter - but it was about £600.

Following that I bought a cheap (about £60) SDS mains drill for work, and that was excellent as well.
 
Last edited:

MaxHeadRoom78

Well-Known Member
Most Helpful Member
Yeah, this have changed since my start out days, Drill Rawlplug holes for fixtures with a hammer bit !. o_O
'Chasing' brick walls for sheathing with a lump hammer and cold chisel.

Hammer drills

1660234392527.png
 

throbscottle

Well-Known Member
I've long thought of getting a SDS drill but I've never encountered anything the Bosch (which is actually my wife's drill. After I parted company with my Wolf one I only had battery drills of my own. But I digress) can't handle. So there's never been any point. And (apart from just having died on me) this one is bloody good - absolutely nothing (else) wrong with it.
But yeah, I'll try shorting out the controller first. 4 wire jobby.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I've long thought of getting a SDS drill but I've never encountered anything the Bosch (which is actually my wife's drill. After I parted company with my Wolf one I only had battery drills of my own. But I digress) can't handle. So there's never been any point. And (apart from just having died on me) this one is bloody good - absolutely nothing (else) wrong with it.
But yeah, I'll try shorting out the controller first. 4 wire jobby.
If you ever drill brick, stone or concrete - you NEED an SDS drill - not having one is like trying to do electronics without a soldering iron, meter, or scope :D

The difference is absolutely staggering.

If you don't drill any of those, then no need.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
So I was wondering if anyone knows a likely cause?
Check the resistance across the brushes while turning the armature one segment at a time, as it's possible there is an open circuit somewhere.

Also check the com still has undercuts between segments, as raised insulation could cause problems?
 

throbscottle

Well-Known Member
Yay, temporarily fixed!
You were all approximately right. The brushes have a short pigtail, so despite there being nearly a centimetre of brush left, they just couldn't go in any further. So I've wound the ends down the springs a bit so it can at least work until I get some new brushes.
Thanks for making me look harder :)
 

shortbus=

Well-Known Member
Most Helpful Member
If you ever drill brick, stone or concrete - you NEED an SDS drill

Why? I've been using my regular hammer drill for years to drill those things. Maybe SDS means something different in the UK though.

SDS in the states is a type of drill shank, not a drill motor its self.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Why? I've been using my regular hammer drill for years to drill those things. Maybe SDS means something different in the UK though.

SDS in the states is a type of drill shank, not a drill motor its self.

SDS is indeed a type of shank, but it's also a completely different type of action. A normal hammer drill hammers small amounts at a high frequency, an SDS drill essentially chisels like a road drill (or indeed the manual drill in post #11), large chiselling movements and rotates much slower - the end of the bit is also entirely different, SDS drills are really crude and blunt.

Unless you're drilling really soft walls, then an SDS is just so much faster - probably 5 to 10 times faster, and will even drill walls that hammer drills won't even touch.

If you get the chance to compare them, you will be amazed.

I did see a video on YouTube, supposedly showing you how to do 'something' (I can't remember what) and the idiot doing it fitted an SDS drill bit in a normal rotary/hammer drill - he then went to get another drill bit (as it didn't drill), and came back with another SDS drill bit :D
 

Pommie

Well-Known Member
Most Helpful Member
By SDS drill I assume you mean a percussion drill as opposed to a hammer drill. I have a Dewalt 24V SDS percussion drill and it's like you said, like a knife through butter.

Mike.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
By SDS drill I assume you mean a percussion drill as opposed to a hammer drill. I have a Dewalt 24V SDS percussion drill and it's like you said, like a knife through butter.

Mike.
Yes, same thing, but over here - no one ever calls them percussion drills :D

The difference is unreal isn't it?.
 

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