The missing drive key slot

[Topper]

Was given a circular saw a few years ago when a friend's father died. I have used it ever since when the need arose. Last week I spent three days building a frame over a friend's new patio and we were cutting some serious wood, 4"x4" posts and 6"x3" and the saw blade stopped driving whilst the motor was still running. Today I decided to strip it down and having spent 20 years in textile and light engineering, prior to returning to study I. T. in 1993, assumed I knew enough about engineering to be able to determine the cause and possible solution to the problem. Having stripped and cleaned all parts I was somewhat bemused when I discovered the reason for the lack of drive. Somehow I have been using a circular saw that has no key slot in the motor drive shaft. Confuscious says, no slot and no key then no drive. Has anyone any idea what was driving the saw initially as for the life of me I can see no explanation as to how it could even cut through butter in it's current state.

 

[Lazarus]

Hard to tell just from the pic, but is it not t'other way around? The component on the right looks to have a key slot, so could it be that the drive shaft had a male protuberance (Yes, yes, I know ..... ) that engaged with the slot - but said protuberance (dog?) has worn away or broken off?

 

[Terryl]

Hard to tell as the shaft in the one photo is a bit out of focus..., it could of had a small key-way milled into it, and the gear has sheered it off, by the looks of the junk around the bearing that may have been the case.

Any indication of this possibility? Maybe showing some photos of the sides of the shaft??

 

[Topper]

Hard to tell just from the pic, but is it not t'other way around? The component on the right looks to have a key slot, so could it be that the drive shaft had a male protuberance (Yes, yes, I know ..... ) that engaged with the slot - but said protuberance (dog?) has worn away or broken off?

Well as the shaft goes through the centre of the windings armature I sincerely doubt it could be manufactured on a lathe with a protuberance and would have expected a key slot and key of which there appear to be neither. Even if a woodruff key had been used there would still be evidence of a slot at some point on the shaft even if the key had dissolved into thin air. I will however have to employ some delicate use of my Dremel to achieve just that fix, if at all possible

 

[Topper]

Hard to tell as the shaft in the one photo is a bit out of focus..., it could of had a small key-way milled into it, and the gear has sheered it off, by the looks of the junk around the bearing that may have been the case.

Any indication of this possibility? Maybe showing some photos of the sides of the shaft??

Well here we are, obviously there is scoring as the shaft was turning at high speed and the gear was stationary, friction generating heat, but no sign of any keyslot

 

[jeallen01]

Frankly, "Performance Power" was a budget brand sold by (IIRC) B&Q and so I suspect that "corners were cut" in the design and manufacture of tools under that name.

 

[Terryl]

It may have been a stamped or forged part, and the key way that was there has sheared off, the resulting friction and scoring has obliterated where it may have been located.

Good luck trying to find new parts for something that old....If you have access to a metal shop you might get a new one made if you want to save the saw, or maybe a look around for a scrap one from somewhere, parts could be found for it that way.

 

[Topper]

It may have been a stamped or forged part, and the key way that was there has sheared off, the resulting friction and scoring has obliterated where it may have been located.

Good luck trying to find new parts for something that old....If you have access to a metal shop you might get a new one made if you want to save the saw, or maybe a look around for a scrap one from somewhere, parts could be found for it that way.

I will attempt some kind of fix possibly as I mentioned above, but it appears to have hardly done any work looking at the wear (or lack of) on the gearing, I would imagine replacement parts would be out of the question.

 

[jeallen01]

I will attempt some kind of fix possibly as I mentioned above, but it appears to have hardly done any work looking at the wear (or lack of) on the gearing, I would imagine replacement parts would be out of the question.

Replacement parts are almost certainly unavailable, and specially-made ones would probably be as/more expensive than buying a brand new tool - so, unless you are "sentimentally attached" to that saw, then it's time to buy a new one and that will have a warrantee !

PS: that shaft is almost certainly part of the motor armature - and so "fixing" the problem would mean building up the damaged part and then machining to the correct shape, or finding (if you can??) a complete new motor armature....

 

[Topper]

Replacement parts are almost certainly unavailable, and specially-made ones would probably be as/more expensive than buying a brand new tool - so, unless you are "sentimentally attached" to that saw, then it's time to buy a new one and that will have a warrantee !

That would be a last resort, far to much ends up in landfill these days, it is far too easy for folks to take a short cut and buy new, I am hopeful all my benchwork experience gives me the impetus to at least try a repair

 

[Analoguesat]

Make sure the blade is on straight & weld it on.

 

[jeallen01]

Make sure the blade is on straight & weld it on.

 

[Topper]

Make sure the blade is on straight & weld it on.

Well your frivolous solution for me is a non starter as unfortunately an arc welder is not a piece of equipment that I possess (unless someone has one going buckshee) although forty five years go I did lots of bench welding abroad. It is however not such a daft idea to either build weld up on the shaft and grind it down to the required depth to fit the key slot in the gear wheel or weld in a replacement key and grind back using the Dremel, I would have to anneal the result to harden it though and this may damage the windings, still rather than bin it, what have I got to lose?

 

[Terryl]

What I have seen done is to first locate where the key should be, then drill a hole to counter tap a set screw in place of the key, the set screw could be a bit bigger then the slot on the gear, a little file work and you may have a fix for it. Be sure to use some thread lock on the set screw.

 

[Channel Hopper]

Well your frivolous solution for me is a non starter as unfortunately an arc welder is not a piece of equipment that I possess (unless someone has one going buckshee) although forty five years go I did lots of bench welding abroad.

Pit looks like an ideal candidate for a friction weld (only one pair of mole-grips required), and this might have been how the saw was constructed in the first place.

 

[jeallen01]

Pit looks like an ideal candidate for a friction weld (only one pair of mole-grips required), and this might have been how the saw was constructed in the first place.

Just had a look at another cheap circular saw that I inherited from my father-in-law, and seems to have been made in the 1980's/early 1990's - the blade seems to held in place with a bolt into the end of the armature shaft and which clamps a small plate hard onto it ( a bit like most angle-grinders). Couldn't release the bolt because I don't have, or at least couldn't find, a 2-pronged tool to fit into the clamp plate to keep it stationary whilst undoing the bolt (this saw has no spindle lock like some similar tools).

However, I suspect that this saw simply uses the clamping force from the bolt + plate to stop the blade spinning freely.

 

[Topper]

I am pleased to report the saw is back working again, the drive stub did appear to have the key as part of the shaft, I have created a new keyway and ground a key from some keysteel, I am unsure how long it will last but it is not used that often to be honest, although a replacement would only have cost about £40 from Argos
Strangely enough when I hammered home the key steel it looks crooked, but is not going anywhere anytime soon.

 

[Terryl]

Ahhh GOOD work, another one saved from the dust bin, and it could be twisted as the other one sheared off, could have messed with the key-way..

 

[Topper]

Ahhh GOOD work, another one saved from the dust bin, and it could be twisted as the other one sheared off, could have messed with the key-way..

Lol there was no keyway which is how and why I started the thread with the title 'Missing drive key slot' I created the keyway using my Dremel and a fine cutter, finished off with a square microfile

 

[Terryl]

I usually finish things off with about half a bottle of scotch.....But if the gear had a key slot there should have been a key and key way......Right????