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Old 18th Oct 2021, 8:36 pm   #1
GMB
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Default Bosch CSB 850-2RET hammer drill

I am struggling to repair (again) this hammer drill. The problem is that the motor is not going round very well (feels stiff and lumpy) so either something is stuck in it somewhere or the bearing at the brushes end is damaged (maybe this).

The problem is that it will not come apart. As best I can tell from a video in Russian, after the gearbox takes off (done) the rest of the gearbox should just pull off taking the rotor and end bearing with it. But it is stuck and I can't see why or how to sort it.

My worry is that the bearing has got hot and glued itself to the plastic that holds it. The brushes end is just a part of the plastic body, so nothing to take off.

This job has just gone up in significance as I discover that drills of this specification no longer exist!! So I am reluctant to enter the "do or die" phase until all avenues have been explored.
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Old 18th Oct 2021, 9:59 pm   #2
Leon Crampin
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Default Re: Bosch CSB 850-2RET hammer drill

I repaired a Bosch hammer drill recently which had all but seized solid. On examination, the field permanent magnet segments had become unstuck from the yoke, resulting in a virtually locked armature.

Fairly strong measures were needed to unstake the yoke from the brush plate in order to withdraw the armature. The yoke bore and magnet segments were then cleaned up and re-assembled with warmed long set Araldite, paying careful attention to the magnet indexing relative to the brushes. Some jigging was needed to hold the magnets correctly during adhesive curing.

The job was a complete success - but took some time.

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Old 19th Oct 2021, 7:51 am   #3
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Default Re: Bosch CSB 850-2RET hammer drill

That would explain the feel of mine, except I do not think it uses permanent magnets as I can just about see a field winding. It is quite old (although it doesn't look old).

But contact between rotor and stator could be the problem. If only I could get the rotor to come out!
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Old 19th Oct 2021, 8:11 am   #4
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Default Re: Bosch CSB 850-2RET hammer drill

I think you may have already seen this but just in case.. https://www.mtmc.co.uk/Bosch-CSB-850..._p-154457.aspx It looks as though all parts are (were?) available separately which implies it should come apart....good luck with it.
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Old 19th Oct 2021, 8:27 am   #5
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Default Re: Bosch CSB 850-2RET hammer drill

Yes, that diagram is on several web sites. It shows the big chunk 843 separate from 825. 825 comes off easy (don't loose the ball). But clip 54 seems to pin the rotor to 843. In a video of a similar model it looked like one expects 843 plus the rotor to lift out. The tail bearing 13 comes out with it all so it must just be a push-fit into the plastic back-end, as you can see that nothing much comes off there.

But mine is stuck. 843 is loose relative to the body but only moves about by 0.5mm or so. The rotor shaft does not wobble about at all at this point.

What the diagram doesn't show (well actually it does) is that all the wires are white so you have to be super careful taking the back end stuff off - but I have been here before.
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Old 21st Oct 2021, 8:04 am   #6
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Default Re: Bosch CSB 850-2RET hammer drill

Update: the end bearing is indeed stuck to the plastic case. It needs to come out to be replaced.

Any ideas for freeing it up?

I am having no luck with this so far.
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Old 21st Oct 2021, 11:53 am   #7
mark_in_manc
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Default Re: Bosch CSB 850-2RET hammer drill

Work out where the centre of the motor shaft should be (!) in the rear plastic housing - drill a small hole from the rear aiming to hit the middle of the shaft axially, then put a pin punch in and tap out the shaft and bearing? Plug the hole later with filler.
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Old 21st Oct 2021, 6:15 pm   #8
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Default Re: Bosch CSB 850-2RET hammer drill

Maybe just class it as "beyond sensiblle repair", lob it into the nearest wheelie-bin and buy something new, with a warranty and rather more-efficient from Screwfox/Toolsatan/Machine-mart?

It's in no way a 'Classic' power-tool.



The older I get the less-time I am prepared to spend on fixing these noise-level things.
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Old 21st Oct 2021, 6:44 pm   #9
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Default Re: Bosch CSB 850-2RET hammer drill

I have a similar Bosch drill that belonged to my late FiL who was an electrician.

I can't get to it at the moment to see the model, but for drilling masonry I prefer my cheap Lidl "Parkgate" SDS.
I know it won't last anything as long as the Bosch but SDS trumps chuck-hammer for performance.
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Old 22nd Oct 2021, 10:04 pm   #10
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Default Re: Bosch CSB 850-2RET hammer drill

Quote:
Originally Posted by mark_in_manc View Post
Work out where the centre of the motor shaft should be (!) in the rear plastic housing - drill a small hole from the rear aiming to hit the middle of the shaft axially, then put a pin punch in and tap out the shaft and bearing? Plug the hole later with filler.
Thanks for that. I have tried this but it will not move. It is difficult to hit it very hard as there is nothing to drive against, because I am driving the whole end section off along with the rotor.

I have tried to think of a way to make a puller to do it but again it is hard to find a part of it that is strong enough to take the force.

Quote:
Originally Posted by G6Tanuki View Post
Maybe just class it as "beyond sensiblle repair", lob it into the nearest wheelie-bin and buy something new..... It's in no way a 'Classic' power-tool.
Well that would be good, but as I said I am not finding drills with the same specification from any source at all.

The world seems to have gone for Li-Ion but I do not see them as a replacement for something that I have used for extended wire-brushing or very heavy duty drilling.

So show me a quality drill of ~850W (importantly the reliable maximum that my 1KVA generator can run) with 2-speed gearbox, hammer, proportional control with reverse, the ability to set the maximum torque (very useful) and with key chuck (I do not get on with the modern kind). Many manufacturers seems to have given up on the (expensive) geared 2-speed aspect and the torque setting feature seems very rare. A classic "they don't make them any more" it would seem.
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