Power drill or SDS that will run at roughly a fixed RPM

[Steve Walker]

Isn't the point that neither can run *continuously* at low speeds without overheating.

SteveW

[James Harris]

I don't know. I know that's been suggested. I don't know that it's been established. In particular I don't know if it's relevant to the use I would make of it and I don't know whether it would apply to all makes and models. Maybe it would apply to cheap ones. Maybe expensive or powerful drills would be fine. People used to use drills to run lathes which turned continuously for a while. Maybe drills were built to be more robust then. Maybe not. I don't know. Hence the questions.

[James Harris]

Thanks. That's useful to know.

I might buy a drill from Screwfix as they have a good returns policy. It will almost certainly run at a similar rate to your Ryobi but if not, I will at least be able to take it back.

Too late!

I have an old washing machine and have wondered if its motor and belt drive could be used, perhaps coupled to a speed controller. But it would take me far too long to work out the required winding.

Your suggestion of a mixer motor looks good. If the drill-based solution doesn't work, which parts of a cement mixer were you thinking I would need to buy? Just the motor, or motor plus gearing?

[Steve Walker]

The problem is that at low speeds the cooling fan is running too slowly to properly cool it.

Industrial variable speed motors needing low speed operation often have a separate motor to drive the cooling fan. Alternatively, if they don't have to go too slow, they are engineered to have oversized fans and lots of cooling fins - which is obviously impractical for hand-held tools.

SteveW

[Dave Plowman (News)]

If size isn't a problem, the top part of a cheap pillar drill? Which includes pulleys to give the sort of speed you want? They cost about 50 quid new.

[James Harris]

That's a good idea. I just checked a few, though, and their lowest speed is 180 RPM - about twice what I expect I'll need.

I checked guidelines for lathes too. Again, unfortunately, their lowest speeds seem to be quite a bit faster than needed.

[Dave Plowman (News)]

Probably quite easy to get suitable sized pulleys to give you the speed you want.

[James Harris]

Where from?

I have been down that road but with little success. The local engineering firm suggested 4 x pulleys shafts including machining etc with motor and belts c £490. Plus VAT. The machining was, I believe, to put keyways in the shafts so that the pulleys would not slip.

[Dave Plowman (News)]

Of course a machine shop is going to give the easiest way for them to do things - since you're paying.

You'd need to check various engineering suppliers to find out what pulleys etc are available.

Or look for a used induction motor with gearbox that gives you the sort of spindle speed you're after. Ebay, etc.

[John Rumm]

Places like machine mart sell pulleys off the shelf in a number of diameters and bores.

[newshound]

All sorts on eBay too.

[James Harris]

I tried them. Unfortunately the local store explained that they sell only the pulleys. They don't sell shaft and bearings etc. Their explanation was that they sell pulleys purely to go on the shafts of their motors.

[James Harris]

...

That's a good idea, though I suppose you need to know what to look for. If you were going to search Ebay for suitable shafts and bearings and a means of attaching pulley to shaft and shaft to bearing what search terms would you use?

[newshound]

Several options. Pulleys:

Most common use a keyway so you would need suitable shafts. Custom machining is expensive unless you can find a friendly DIY type with access to a milling machine. Model maker, steam engine restorer? Engineering apprentice?

Some come with clever clamps held with hex socket grub screws. Convenient for adjustment, a bit more expensive.

Some just have grub screws engaging in a conical hole in the shaft.

For your application you could just drill the pulley and shaft, and fit with a roll pin.

For shafts to fit in rolling element bearings, easiest option would be silver steel (eBay).

Ball bearings ready mounted, look for Plummer Blocks (eBay).

Cheap imported ball bearings might be no more expensive than bronze bushes.

As long as you keep them lubricated, you might get away with steel shafts running in brass bushes made by drilling out suitable plumbing fittings to suit your shafts. (The point is, it is easy to mount something like a bulkhead fitting on a random bit of plate).

[newshound]

You might get away with mild steel round bar, from eBay. Or a friendly blacksmith.

But as I keep saying, I would try to adapt something which already exists, not build it from scratch. Some council tips will let you scavenge things.

Various old Belle mixers on eBay from £40 (check voltage)

[James Harris]

What about fitting a shaft to a Plummer Block (or to some other bearing)? Do they need to be pushed into place with a large pusher, or are they tapped into place, or do they lock in in some other way?

[tabbypurr]

No way is that going to work by slowing the motor down - far too much torqu e required at far too low rpm. You need gearing. Or to be more precise, you need to use something able to run for long enouh to do the task, a drill m otor is far short of being rated for continuous operation.

NT

[tabbypurr]

You're not liekly to get much good advice until you take a step back and realise there are basic problems with the design from the start.

NT

[James Harris]

I've been given plenty of what seems to me to be good advice.

[James Harris]

How long are you classing as "continuous" and what would happen to a drill which is run too slow for longer than the period you have in mind?