Kennedy Hacksaw bearing replacement

I'm in the process of rebuilding a very scruffy Kennedy powered hacksaw, and find that the main shaft bearings are very worn - especially the long main one attached to the base.

The bearings are plain - and nothing fancy, in fact they look more like copper tube. I'd like to change them, probably for Oilites. Has anyone replaced them, and if so, were they just pushed in? They look well seated, and so I'm just hoping they are replaceable and not somehow cast into the alloy, like some of the other fitments on the saw!

Any experiences or guidance would be most welcome before I just have a go!

All the best
Graeme

Even if the bearings are cast in, they pose a little project of ingenuity in boring them out and turning up replacements should be easy in comparison.

At worst, keep reaming out until there is nothing left of the original?

Howard

Graeme,

What a coincidence I have just bought a Kennedy too, luckily the bearings are good, but the hex slides are worn. Being cast in there is no chance to replace them.

What state are your slide in?

Adrian

Adrian

Concerning your worn slides can you not simply machine the top of the blade carrier and bottom to the upper sliding part so they can be bought closer together to take up the wear.

As the stroke is always the same the wear on the main slides will be even. However the unworn portion beyond the active area may foul the blade carrier and upper slide when they are moved closer together. As that unused part of the main slides is in the wind and purely structural in function there should be no problem in machining that part for clearance.

As I recall matters the Kennedy we had in our local departmental workshop had its slides adjusted to compensate for wear.

Clive

The slides on mine are self adjusting, in that the bit of hex bar which sits above the blade frame, is spring loaded rather than adjustable in the sense of a gib strip.

I have the same problem with wear in the bushes, which I'll address eventually, but my main problem is the belt tracking. The driver pulley just doesn't lime up with the large alloy pulley; not that they aren't parallel, rather that the crowns on the two pulleys are offset with respect to one another. It's almost like the motor spindle isn't long enough.

There isn't any adjustment on the motor end, as it rigidly held with 4 allen bolts.

I think I'll probably devise a conversion using a poly V belt drive, but I'm not sure if I will be able to get a low enough drive ration in a single stage.

Bill

Edited By peak4 on 16/08/2019 10:41:03

it's easier to file or grind clearance on the top slider and the blade carrier, for some reason the wear is not even (like car piston bore wear you need to avoid the step with 'step dodger rings' if you just fit plain new rings the step smashes them) and simply adjusting the slider makes the carrier stick if you dont.

The wear I have is not uniform, the blade carrier and top piece are both convex, and the rails are worn more one end/side then the other. Max wear 0.19mm.

My plan s to mill them flat as soon as I can work out how to hold them at the right angles. Not sure how well it will work on my mill as it is not robust and I will have to use the side of an endmill.

Spring loading the top part sounds like a good idea, I would like to see some pics of that.

Adrian

It's out in the garage at the moment and tea's about to be served, but a very simple arrangement.

When I got it he top bar was held on to the saw frame by a couple of allen screws. The top bar itself, was counterbored and a small spring fitted around the shank of the allen screw.

I've since replaced the allen screws with loctited studs and used a nylock nut above the springs, rather than the allen head. The original arrangement kept working loose.

Bill

Seems like I started a list of woes here by asking about the worn bushes! My slides looked reasonably OK - a bit scored, and with small burrs on the corners of the hex at a couple of points - but not obviously worn. I was planning on filing the burrs and just cleaning up the faces. That said I think I now need to measure their "across face" dimensions and see how that stacks up. I'm away right now but I'll have a look when I'm back. Maybe I'll have the same problem myself!

I don't suppose the hex bars are hardened in any way - case hardened maybe? Otherwise they would surely wear pretty quickly, especially since similar hardness materials acting as bearing surfaces are not generally recommended. Just a thought.

Until i look at my own slides however, it doesn't sound like anyone so far has tried to change the bushes. I thought I'd try making up a small press-piece on the lathe that fits the I/D of the bush with a step slightly less then the bush wall thickness, and see if it can shift them with a bit of vice pressure. That at least will tell me if I need to bore or ream them out.

Graeme

So, a bit of feedback;

Bearing Bushes - I was able to push out the scored bearing bush from the casting which includes the two hex saw slide rails. I can't completely decide if it was cast in place, but the cavity it left behind in the casting was clean and shiny, and will easily take replacement bushes - so my guess is that it wasn't cast in. The bearing that came out was a piece of bronze tube 2" long. I am going to replace this with two flanged oilite bushes (3/4" I/D, 7/8" O/D, 1/2" long, 1/16" thick flange) one pushed into each end. The 1/16" thick flange is about the same as the amount of bronze tube that was left protruding from the casting, and provides spacing against the mating components. I would have liked longer bushes, but they simply don't seem available in this size in the UK. But the loads involved I am sure will be taken up perfectly well in two 1/2" bushes. And the gap between them within the housing will act as a lovely oil reservoir! I decided not to change the two shorter bushes in the other casting, as these appear to be in better condition - almost no slop. If they prove to be an issue I can always change them later.

Saw slides - I measured across the faces of the hex sections which form the saw slides. The worst wear I could measure was a loss of 0.15mm, with 0.10mm wear more commonplace. The working faces had a bit of scoring on them, but that was all. I feel this is not going to cause me any problems, and I will just lap the faces to make them smooth again. I am assuming that if I can keep the 60 degree angles accurate, then the faces will mate correctly, under the adjustment of the fixing screws - or a spring as previously discussed. I don't see any need to mill mine certainly - some emery on a surface plate should do the trick.

Drive belt - my belt and the motor pulley were missing from the saw I acquired, so I need to address this. I was going to make a small diameter motor pulley with a crown and get a flat belt - as in the original. I know however that these can be prone to slippage. Then I found an interesting video on Youtube showing how an enterprising chap and used a Poly-V belt to address this slippage on his Kennedy saw. He made a parallel motor pulley with the appropriate multiple vee grooves, deployed a Poly-Vee belt, but ran that on the original crowned big pulley. His belt was as wide as the crowned pulley could accommodate. I guess the small motor pulley is where the slipping occurs, it being only about 25mm in diameter, and close to the big pulley - so little wrap around of the belt. Slippage on the large pulley is likely not an issue. So, my plan is to replicate this setup. All I need is to grind an HSS lathe tool appropriately for the vee shape of the Poly-Vee belt!

Drive Belt Cover - mine is missing. I don't suppose anyone out there has an old spare one lying around....?

Any thoughts or comments are very welcome!

Graeme

You could of course "fill the gap" with a plain bearing of appropriate size?

Graeme,

Thanks for the info about the bearings, never know when I might need to change mine.

The un-powered version of the saw was sold with a 4 1/2 " V pulley and it says it should run at 240RPM.

I found this site that has information about the Kennedy.

Adrian

Thanks, chaps.

I did wonder about filling the gap with a plain bearing - in fact I could cut off some of the old bearing tube and re-use that, just to reduce the amount of space being left as an oil reservoir. I'm not sure it's necessary, but as ever there are options!

I think the issue with the "powered" saw is that the small pulley is 25mm diam, and the large pulley is around 150mm diam - a big difference, plus they are very close together. That means there is little wrap around of the belt on the motor pulley, and traction is limited. On the un-powered version, if the motor is mounted a way from the saw pulley, then there would be more wrap around, and hence more traction available. A traditional vee pulley however can't really work on the powered version as the pulleys are just too close together and the belts aren't that flexible. I think those that have gone the vee pulley route have had to use link belts to get it to bend as tightly as it needs to! But I reckon a Poly-Vee - which is thin and flexible - could be just the ticket. Best of all worlds.

Graeme

Videos of Kennedy hacksaws always seem to be ‘fast and furious’. The Edgar T version (Hemingway kits) run at a more leisurely pace at around half that speed?

240 rpm with 4” stroke equates to only 80fpm cutting speed, but they just seem to be very fast.

At that sort of power level Poly-Vee belts run just fine on adequately sized flat belt pulleys.  Vee side down.  Commonly advocated by the SouthBend fraternity. Certainly worked just fine on my Heavy 10 once I'd nailed the belt joining technique.

Motor pulley is small so probably makes more sense to buy one of appropriate size than make one. Although I found making an unobtanium 3/4" diameter one for something electric easy enough using micrometer bed stop to get the groove spacing right. Probably a right pain without a micrometer stop or DRO tho'.

A nooge around the belt suppliers websites should unearth a catalogue with length calculation formulae. I found them very accurate 5 to 10 years back when I had a bunch of Poly-Vee jobs. Certainly better than the usual Vee belt ones. Even so its unlikely that you will find just the right size belt. Either add a spring loaded tensioner device, which will also increase the belt wrap on the motor pulley, or make the motor moveable to set belt tension. The spring tensioner has worked fine for me on various jobs. Basically two cheap ball bearings in a tube for the roller and, usually, a motorcycle stand spring. Or just use a slot and locking bolt to fix the arm.

I'd always understood that the limited belt wrap on the motor pulley was intended to act as a simple power limiter so the saw would stop rather than break the blade if things jammed. The one at work got used a lot for cutting 1" square "speed frame" tube by various unfeeling folk and got jammed on a regular basis once the blade got worn but never, to my recollection, broke blade. Wore out plenty tho'. Never could get the unwashed to understand that when the teeth are more or less gone changing the blade is desirable.

Clive

Edited By Clive Foster on 19/08/2019 18:50:10

Graeme,

Bearings are available, go to the Bearing Boys website and look in imperial plain oilite bearings. They have a 3/4" ID x 7/8" OD x 1 inch long oilite, plain not flanged. Part number A11214-16 price is £3.96 each. They may even have 3/4 inch long but I didnt check that far. I was on their site looking at something else so thought I would check if they had the oilites you were after whilst I was there.

Many thanks for the reassurances, Clive. I don't have much experience with these belts above one being used on my wood lathe! But it certainly seems like the way to go. Having had a look round, they seem to come in 1" increments in length, so some level of adjustment or tensioning seems important to design in. On the Kennedy, the motor is fixed but there are slotted fixings in the base where the main components are attached - so a small degree of adjustment is possible there. I guess I'll just have to by the nearest I can - as measured with string - and then work out the details once I get there!

I think however I will have to make my own pulley for the motor. At 25mm diameter on a 5/8" shaft, I have found absolutely nothing available off the shelf - not even close. At this diameter, it also doesn't offer a lot of "meat" for a grubscrew. Added to this, the motor shaft is only about 28mm long, which is broadly the width of the belt I was planning to use - the big pulley is 27.4mm wide, and so I was aiming for a 10 rib J section Poly-V belt to use all the width and get the maximum grip.

Could I get away with a narrower belt and it still grip sufficiently on both pulleys? That would help if I could.

But if not, then my best idea so far is to make a suitable 25mm diam Poly-V pulley, put one or two grub screws in the main body of the pulley, right where the V grooves are, but obviously below the level of the V grooves themselves. And then maybe cut a keyway in the pulley to add some mechanical grip, so we're not relying on the grub screws to drive the machine. The original motor shaft already includes a keyway, so a short key alongside the grubscrews would seem like a good idea. Though a lot of effort.....

Or am I overthinking this?

Thanks for your note too, Ron. I had found the plain Oilites, but really wanted to use a flanged type as it gave me the precise spacing I was looking for. As ever though, more than one way to skin a cat - and maybe a couple of 1" plain bushes back to back would have been the way to go. My flanged bushes were already on order though, so whether I made the right call will be found out soon enough!

All the best
Graeme

There is nothing stopping you using a loctite, or similar, product to help secure a small drive pulley. One which does not require too much heat to enable removal?

Tumble dryers and washing machines use very small drive pulleys with fairly extreme wrap around, spring-loaded adjusters and ony 16-20mm polydrive belts as I recall.

Machine now going back together, with the flanged bushes fitted nicely. All good - I did have to make and deploy a 0.5mm thick washer on the shaft, to take up a tiny bit of play between the fixed and moving bushes - but that seemed like an OK thing to do.

Latest discovery is that one of the two bolts that fixes the main casting to the base is short! And is stuck fast in the main casting. How can this be? Looking from the front, the left hand bolt is as expected and goes through both castings with plenty of length for a nut and washers. But the right hand bolt is of larger diameter, and fixed permanently into the top casting. It is just long enough to go through the base casting, with maybe one thread protruding - not enough to get a nut onto it!

When I dismantled the saw I hadn't noticed it was short - though I do recall it all coming apart slightly prematurely as I loosened the other nut, so I am guessing the second nut wasn't there. I can't see how this is right. Maybe someone has tapped or driven the right hand bolt into the casting as a bodge when the proper bolt was lost? Not exactly a workable solution as the saw swivels on its base, but you never know!

I'd really appreciate it if a Kennedy owner out there could take a quick look at their machine and just see if identical nuts and bolts are used on both left and right hand sides? If so, I will give the stuck bolt a bit more heft to get it out - and replace it with a proper sized bolt.

But it would be good to be sure what I have definitely isn't right before I go and break something!!

Graeme

Mine has 2 identical M8 bolts passing through holes in both castings (saw and base)
They look clean, and are fitted with self locking flange nuts, so I presumably replaced them when I got the saw from my local scrapyard.

I presume you have looked at the photos on Lathes.co.uk

Bill