Kennedy Hacksaw

I'm trying to bring this model to mind. Is it the bench top saw? A picture would be useful if you have one.

There needs to be a way for the oil to get around the piston or out of the cylinder, and this is not normally by leakage around the sides of the piston (at least not in any saw I've seen). Is there a valve in the piston which could be jammed or incorrectly adjusted?

If it's the small machine I'm thinking of, which takes ordinary hand hacksaw blades, I'd say it needs roughly a 1/4 hp motor. If it's a big, old single phase motor, keep it. They're generally very well made.

Best wishes,

Chris

OK Here are some pictures.

There is a valve - there is a thin plate below the piston which closes the holes in the piston - it can be held away from the piston by a threaded adjuster which screws into the piston. It wasn't jammed - in fact it didn't work as the plate was bent by having had the adjusting screw done up too far. I don't think that was me so it might suggest previous difficulty.

I'm sure the intention is for the oil to go through the holes in the piston but I'm wondering about the piston tolerances especially as the dashpot seems to have been put into the mould as it was cast.

I'm sure it's well made - it's just very heavy - I'm wondering whether I can install it below the bench and just connect the belt when I want to use the hacksaw.

Thanks for looking.

Russell

Forgot the link:

I know absolutely zilch about Kennedy saws but am always ready to make comment. (and probably make a fool of myself )

1 I would have thought that the L shaped bar that is central to the piston is the one that goes through the hole in the raise/lower casting. (Actually I can see now that the other bar is not L shaped but off at 45 deg or so, so ignore this bit.) 2 I would expect to see a light spring between the flapper plate below the piston and the head of the bottom screw 3 I would expect the other (offset) L shaped bar (now seen as 45 deg) to be screwed into the piston until it nearly touched the flapper plate. A twist on this would then break the flapper plate seal allowing oil to escape to above the piston therefore lowering the head until at the correct point an "unscrew" will recreate the seal. The head will now fall solely due to oil leakage around the piston. After cutoff a twist would allow the oil to pass through the piston allowing a lift of the head.

But I may be wrong Grade of oil used, probably EP90 or something similar, maybe thinner depending on wear.

None of the above answers your piston dimension problem I would manually position the (oiled) piston in the pot and rotate whilst rocking to the degree you would expect in service. if you find a point that looks acceptable then mark piston to pot and lock up the L shaped bar to give this position when in service. If you still cannot find a working position then remove the piston and refit the other way around and retry.

Best of luck.

Richard

I don't know if its any help to you, but here are a couple of pictures of my Kennedy saw showing how the dash-pot is linked.

Thanks Gary

Pictures are always helpful - just having a look at another machine helps to spot things that aren't as they should be. In this particular case I note that mine is missing a spring on the knob that needs to be pushed to release the arm.

They also show that I had the mechanism correctly assembled. I have tried as Richard suggested to find a working position for the piston with no success and I am coming to the conclusion that I will have to ease the piston a lttle.

It would be very useful to know how fast the arm on your saw falls both with maximum damping and at your usual setting - and what grade oil you have in it. That would help me to be a bit more confident about the piston sizing.

I am wondering whther the wear has actually deformed the surface of the piston rather than wearing it away so that the area immediately either side of the central ring has been raised slightly. That is the only way I can imagine that this used to work but now sticks really tightly.

Thanks

Russell

Hi Russell, As near as I can judge, minimum and maximum settings give about 0.75 and

2 secs respectively. I've been using about halfway for the (57mm) stainless bar you see in the photos. The movement is very smooth with no sticking at all. I'm sorry, but I've no idea what the oil is - it looks like standard motor oil to me. I confess that I haven't had the saw long - I purchased it at a club bereavement auction and thought it was more of a toy than a serious tool. How wrong was that? It took about 30-40 mins to saw through that bar, but I think it needs a new blade. I just left it chattering away by itself while I did other things.

I hope that helps, but I'm willing to dismantle bits if that would help further.

Hi Gary

Thanks. The arm on mine takes about 30 seconds to descend with maximum damping so it doesn't sound like that's going to be a problem. I used EP90 oil which will probably account for some of the difference.

I think it looks as though it's a useful tool - I don't think 30-40 mins to saw through a 57mm stainless bar is too bad - and I'm sure it'll do it straighter than I can too.

Mine seems to stick a bit - it's much happier with a drop of cutting oil on the cut - or with the spring disconnected.

I'm not happy with the drive yet though, the motor's got plenty of torque but there's no way to tension the drive belt so I clearly need to experiment more - I think my next step will be to try and stop the belt slipping and fit a decent quality blade.

I'll let you know how I get on.

Russell

Hi Russell, A couple more bits of information that might be of use: the motor on my unit, which appears to be original, is a Hoover 1/6HP running at 1425 rpm. The drive is transmitted via a flat belt drive to give approx. 6:1 reduction, ie, about 4 strokes/second. Ordinary lubrication oil helped a lot when cutting the SS bar - I had to cut 3 sections off, so was very pleased not to have to do it by hand!

Them square looking Hoover motors run very hot ..i have three in different machines ..including a three phase one .

when i use any of them for any period of time exceeding half an hour they start to stink of burning shellac.

all the best.markj

Interesting. Are they rated as "Continuous"? Mine is, and it ran for about 3 hours without undue heat or smell - certainly nothing to cause concern.

Hi Gary/Mark

Thanks for the comments.

I had assumed that those motors had some gears in - I had no idea that it was a single stage reduction. I suppose that's why they used a flat belt as the small pulley was too small a radius for a V belt.

That's very useful information though. I tried to tension the belt today and while I was doing it I put the motor on some old bathroom scales. It weighs 27kg. A revised drive system is on the cards! - and it sounds as though that could be simpler than I realised.

I did get it cutting better. I cut a slice off the end of a 1" bar about 1.5 mm thick and I was very impressed that it didn't vary in thickness by more than 0.002". It took nearly 15 minutes though.

It seems to be going a bit slow compared to yours though. I'm a bit surprised at 4 strokes per second - I make that a cutting speed of

125ft/min which I suppose is OK for most things. I timed mine at about 100 strokes/min.

I do have one more question to be going on with - what is the direction of rotation. When the belt was off I tried cutting by hand and noticed that one direction was easier than the other and I can see reasons for either direction.

Thanks again.

Russell

Hi Russell,

Sorry for the slow response. Thanks for the pictures.

It is the Kennedy hacksaw I was thinking of.

Can you pull the piston out of the cylinder, but can't push it in all the way down? If so, it's probably the valve that isn't working.

That steel plate on the bottom of the piston, the one that acts as a valve, looks very thin. Is there any chance it's unoriginal? If it's too thin, it'll flex in service, closing the holes in the piston and stopping oil from flowing through the piston. The Qualters & Smith hacksaw I have uses the same valve design. The valve plate on the Qualters & Smith is about 1/8" thick. Although yours is a smaller machine, I would not expect the valve plate to be as thin as it looks in the picture (it looks really thin, like perhaps 1/64" thick).

I would be cautious about turning the piston down to a smaller diameter. I very much doubt that's the problem. I think it's probably the valve mechanism. They are sensitive to being correctly adjusted.

As for the oil being too thick, it's possible but I doubt it. If you push hard on the piston rod, does it move down slowly or not at all? The Qualters & Smith machine is supposed to take ISO 150 oil in the cylinder. I would expect your machine to need a similar viscosity of oil. And putting in oil heavier than ISO 150 by chance is unlikely.

If you want a permanent installation, you could bolt the motor to the underside of your bench. You could change the pulley on the motor to give you a faster cutting speed. 100 strokes per minute sounds a bit slow for a small hacksaw. My Qualters & Smith machine does either 100 or

150 strokes per minute, and that takes a 16" blade.

Those geared motors are expensive. There was a used one on eBay for about ?200 recently.

Someone mentioned a Hoover motor. I think the Hoover motor was the official motor for the Kennedy saw. I've certainly seen them fitted with Hoover motors before.

Good luck!

Best wishes,

Chris

Looking from the shaft end of the motor it rotates clockwise. When I got the saw the blade was inserted with the teeth pointing "backwards", ie towards the motor and crank assembly, so it cuts by dragging the blade. I don't know if it's correct, but it certainly works, so I've kept it that way round.

I've just discovered that the recommended oil for the dashpot was Wakefield (Castrol) V. Although there is still a Castrol V oil available (20W50) I don't suppose for one minute that it's the same as the Wakefield stuff of the 1950s, but at least it, sort-of, endorses my use of ordinary engine oil.

This page (your source for the oil recommendation I assume) is quite informative:

I can't find any other references to Wakefield (Castrol) V oil online. The only sites which come up refer to Castrol V-Twin 20W/50 oil, which won't be the same thing. I think it's just the search engine finding something similar but irrelevant. I'd suggest you call an oil supplier and ask them to find the nearest equivalent, then get something of the same viscosity. Morris Lubricants in Shrewsbury are pretty helpful.

I'm not sure which way the blade teeth should face. My big power hacksaw has the teeth facing so that they cut on the draw stroke. If there's no powered lifting of the blade on either the forward or return stroke, it may not matter.

Best wishes,

Chris

I've a fairly big Wicksteed saw. Mine works on the ''push'' stroke, so yours may well be wrong, but I can't say for sure.

One thing to check is for correct rotation. On mine the hydraulic pump has two piston plungers and is ''timed'' so that the blade is raised from the cut on the return stroke, if you have the machine running backwards then the timing of the blade lift is all wrong and cutting is poor (and the blade gets the sharpness rubbed off the teeth in two ticks!)

Yours seems very slow to cut, mine will blast through a 6'' RSJ in a little over a minute, it is a bigger machine that yours, but not disproportionately so.

Julian.

Thanks for the comments.

I had seen the lathes.co.uk site. He can apparently supply a manual at £12 I think but I'm slightly reluctant to pay that as it's nearly as much as I paid for the saw. I think Chris has anticipated the way my thoughts are running with his comments about the price of gearmotors. I'm wondering whether I might be able to turn a profit on acquiring this saw!!

I've experimented with turning the blade around and it seems a little bit happier cutting that way but I can't say there's a lot in it.

I read the various comments about lifting the blade. That was one of the reasons I was thinking about with direction of rotation. In one direction the action of the crank tends to lift the blade and in the other it tends to move it down. Because of the friction of the cutting stroke it goes down more forcefully on the cutting stroke. My motor was set to rotate the same way as Gary's. There is no lifting mechanism.

I'm still a bit puzzled by the action of the damper. You're quite right Chris that the plate is very thin but I don't see any sign that it's not original - it would have been much easier to make it thick as it's turned on both sides. It's also a bit bent so it might be possible to improve it's sealing a bit.

I don't have any doubt that the piston was sticking - even with no oil in the dashpot it needed pulling wiggling and twisting to get it out.

I don't really see what purpose it has - it stops you dropping the blade on the work but the cut is slow relative to the fall of the blade so I don't see that it makes any difference while it's cutting. Even with a new drive system I'm not sure that it'll be fast enough to affect that.

As far as a revised drive system goes I've only got a 1/8 hp motor. I'm thinking about stepping that down by 8:1 to get a similar torque to the Hoover motor at 6:1. That should give me about 180 strokes/min. I'm wondering whether I can do 8:1 in a single stage?

Thanks again.

Russell

Just my twopen'orth.

I bought a hacksaw machine from the scrappie about a decade ago. No motor, I used a 1/4hp motor flange mounted onto a worm drive. Worked really well until one day when I'd left it munching away at some crane rail. The vice had worked loose, saw jammed, so *that* smell, and smoke in the roof space on my return. Well, motor starter overloads for that size of motor aren't up to much. If I did it again, I'd fit a microswitch to the slider crank, connected to a (say) 200mS solid state timer - motor turns off if no reset pulse for that period.

Regards,

David P.