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Shortening a Motor Shaft


halfwit

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I have just destroyed a Mashima (1220) motor shortening the rear (brush end) shaft by melting the plastic casing.

I used a cutting disc in a mini drill which obviously produced too much heat. I did put a clamp on the shaft to act as a heatsink, but still the end melted around the bearing.

Has anyone got a better way of shortening a motor shaft? (This one needs cutting down to within 1mm of the end.) Or would a wad of wet tissue on the shaft act as a more efficient heatsink?

I hope someone can help!

 

(I did do a search but I couldn't find anything relevant.)

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Make small cuts and allow metal to cool each time, never had a problem personally. with discs (always use a new one)

 

 

I'd go with the above, I'd just add that I put some copper grease around the shaft and bearing then some masking tape over the shaft and bearing in the shape of a + sign. Then a heat sink on the scrap end your fingers are good for this as you stop when it gets warm.

 

OzzyO.

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Use a piercing saw.

 

The blade runs cool as it is manually operated, is far more easy to control, and does not risk your eyes when the disk shatters.

 

Also the best tool for cutting axles, rail, peco point motor arms and just about every metal cutting task.

 

I'm struggling to think of a good use for a mini-drill cutting disk?

 

The only objection to a razor saw is that they are not designed to cut metal and can blunt easily. A piercing saw blade is designed for the task and has a very fine and thin cut. Using a manual saw is more time consuming than the instant gratification of a powered saw but the results speak for themselves - as you have observed.

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Use a piercing saw.

 

The blade runs cool as it is manually operated, is far more easy to control, and does not risk your eyes when the disk shatters.

 

Also the best tool for cutting axles, rail, peco point motor arms and just about every metal cutting task.

 

I'm struggling to think of a good use for a mini-drill cutting disk?

 

The only objection to a razor saw is that they are not designed to cut metal and can blunt easily. A piercing saw blade is designed for the task and has a very fine and thin cut. Using a manual saw is more time consuming than the instant gratification of a powered saw but the results speak for themselves - as you have observed.

 

You would actually have a hard time cutting the material used for Mashima motor shafts using any sort of saw. I routinely cut Mashima motor shafts down (every day) and the only thing I used is a carborundum disc in a Dremel. I am not saying it can't be done with a saw, but you would be there for a month of sundays doing it, as the material is extremely hard.

 

Unfortunately, Halfwit chose the one motor type in the range where it is easy to melt the bearing housing. The 12 series motors have a very thin plastic area supporting the commutator end bearing, and it is easily damaged by excess heat. The other motors in the range are not as easy to wreck in this way.

 

I would echo what has been said here earlier, use a cut-off disc, but do it slowly, allowing plentry of time for the shaft to cool down, and grip the shaft tightly with a pair of vice-grips to heat-sink the shaft. Speaking from experience, as someone who has destroyed a couple of 12 series motors this way due to being in too much of a hurry.

 

Regarding the disc itself, the usual Dremel disc is a thin disc and as Kenton says, shatters easily. As such, I gave up using these many years ago because of the risk of injury from them. However Dremel also sell a much safer fibre-reinforced disc, number 426B. I buy these in packs of 20 discs, and a pack lasts me around 4 years of constant use.

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You would actually have a hard time cutting the material used for Mashima motor shafts using any sort of saw.

I have done it several times but by no means on a daily basis.

But I will grant you, it takes patience and care, especially to get it started. Also all the usual care not to force it, breaking the blade. But it does work and is much more controllable than the "dremel"

 

I expect, if you are cutting that many, that you have the drill set in a holder and the motor also secured - thus giving a much more controlled cut.

 

Razor saws? - just try one ;)

Hacksaws? - take a closer look at the blade and you will see why.

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There is a very simple answer and absolutely no heat, just use a tile cutting saw, like the Abrafile type, made to fit hacksaws or coping saw frames. These are steel coated with nickel, mixed with carbide dust. They will saw glass and ceramics as well as tool steel. To dress the cut end of the motor shaft, use a diamond needle file, very cheaply available these days.

post-6750-058543800 1286985773_thumb.jpg

Some knife edged, or triangle form diamond needle files will also be able to cut the Mashima shaft as well. Neither the Abrafile or the diamond files will make any heat at all, just dust, which can be kept from the bearing with a blob of Blu Tack or plasticine, carefully removed afterwards.

 

Stephen

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No, the shaft is too hard.

 

As a test, I just tried to cut a piece of shaft using a brand-new fine tooth hacksaw blade, and it hardly scratched the shaft. So if you plan on using a saw, good luck.

 

The Mashima shaft is hardened silver steel, I think induction hardened stock, and harder than most steel saws, only a Carbide dust or diamond file will cut, it will ruin a Xacto razor, or Zuron cutters. Even bolt cutter blades are softer, unless fitted with heat treated tool steel blades.

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  • RMweb Gold

I binned all my carborundum slitting discs after one spectacularly shattered. I now only use the commonly available (Squires etc..) diamond coated discs. They last a long time and cut very well. I've used them on silver steel without problems in the Dremel. I've even trodden on one and it didn't break. IMHO worth the investment £2.50 > £5 each from Squires. Also they're normally thinner that the carbo ones.

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I expect, if you are cutting that many, that you have the drill set in a holder and the motor also secured - thus giving a much more controlled cut.

 

Every Mashima motor I fit to a BullAnt is a double shafted motor. The shaft at the (front) end is usually fitted with a gear or pulley, then the shaft is trimmed back close to the gear or pulley. The shaft at the opposite (commutator) end is fitted in most cases with a flywheel and does not need cutting. The front end of a Mashima motor is fitted with a bearing sitting inside the steel motor case, so there is no chance of damaging the motor with a little bit of heat. The problem is the commutator end where the bearing is contained in plastic.

 

So.. when cutting back the shaft at the front end, I do not have to take any particular car with the motor. Holding the motor in my hand and using the Dremel with the fibre-reinforced disc takes no more that 3 seconds to cut and de-burr. In fact because I do this routinely, I have an older Dremel that is permanently fitted with the cutting disc.

 

I certainly would not use the older style cutting discs that Dremel (used to) sell, as they are plain dangerous, but the fibre-reinforced ones are quite safe. I find it puzzling that Dremel (Bosch) still hand out those dangerous discs with every new kit and don't drop them altogether.

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The front end of a Mashima motor is fitted with a bearing sitting inside the steel motor case, so there is no chance of damaging the motor with a little bit of heat. The problem is the commutator end where the bearing is contained in plastic.

Thanks, that's my bit of learning for today, I didn't realise that they were different.

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Thanks again for the replies.

I have just ordered a diamond trianguler needle file - I'll let you know how I get on. A replacement motor arrived today, I've shortened the front (non-commutater) shaft already with a disc, being carefull not to generate too much heat. But I'll wait untill I get the file to cut down the rear which has to be shortened to within 1mm of the casing.

After reading about discs shattering I swapped my normal glasses for industrial safety ones!

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Wrap the motor in masking tape (to keep any iron filings, dust, etc. out of it) with just the shafts sticking out. Chuck the worm shaft in a drill. Rotate the whole lot at slow/mediem speed and use a good quality triagular file to cut a groove into the other end (waste) shaft. When you have groove about 1/3 into the shaft (.5mm for the 10XX or 12xx Mashimas) you are through the case hardening. Break off the waste end with a pair of pliers.

 

That works every time for me.

 

Jol

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  • 3 weeks later...

Well, I've successfully shortened the shaft on my replacement motor tonight. I used Bertiedog's suggestion of a triangular diamond coated needle file to cut the shaft down which worked extremely well and was nice and quick. Here's a pic;

post-6749-044878500 1288809921_thumb.jpg

As you can see I worked around the shaft with the scrap end held in a pin chuck with the motor wrapped in masking tape. After cutting to length I de-burred the end with the file. Another pic, the motor is resting on the file;

post-6749-088579300 1288810096_thumb.jpg

I was tempted to try LNWRmodeller's suggestion of spinning the shaft in a mini-drill whilst cutting with the file but as the cut was quite close to the casing I decided to play safe. I might try that next time though.

The file came from Eileen's Emporium by the way.

Again, thanks to everyone that replied to this topic.

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