Rapidor power hacksaw

Hi folks.

I've just got myself one of these wonderful machines. However the damping mechanism is missing or non functional.

The dashpot seemed to be full of water when I got it so I thought/hoped it would simply be a case of cleaning out the pot and filling with slide oil. But as that's not worked and, from some old posts on here, it appears there may be some kind of mechanism I'm missing. Also wondering if slide oil is too thin, any recommendations for something goopier?

Anyone have any photos or drawings that may be able to shed some light on the matter please?

Feel free to reply or DM.

Ta muchly

J

By co-incidence, I took my damper apart a few days ago, so here are two photos of the internal parts.

The flat bar pivots in a casting on the underside of the hinged casting on the saw.

The slice of a sphere screws onto the end of the bar. A threaded needle rod, tapered at the tip, screws into a tapped hole in the sphere. There is a bolt (shorter than the one you see in the photos) which screws into the threaded hole in the centre of the underside of the spherical slice and that compresses a spring which traps a circle of aluminium against the underside. The needle is adjusted to provide a tilt on the disc, and the oil flows through the holes in the spherical slice. The rate of descent is controlled by the adjustment of the needle. The main threads are 1/4 Whitworth.

Marcus

Excellent that's EXACTLY what I need thanks Marcus, you're a hero!

J

By all means re-instate your damper but it's not essential IMO.Mine was missing when I bought my Rapidor 30+ years ago but it cuts well. Blade life is OK for my hobby use.

Edited By Clive Brown 1 on 30/06/2023 20:26:09

Spoiler alert, these things aren't so wonderful. I have had three reciprocating power hacksaws over the years: a Spanish machine which worked well I regretted selling it, a Wicksteed that was almost so totally useless I got rid of it asap and currently a Qualters & Smith that will do the job but really needs a lot of work on the hydraulics that I can't be bothered to do. I have recently, for the first time in my life, used a well worn Chinese 4.5" bandsaw, the sort of thing that Machine Mart and a whole lot of other 'badge engineers' sell. What an eye opener! They cut fast, clean and square and leave the lumbering old British reciprocating machines standing. It's on my bucket list to buy one!

Tbh one of the biggest reasons I went for the old donkey saw over a modern bandsaw is that I just love the tune of them at work. I'd happily run it through a bit of scrap just for that. However I totally disagree on the accuracy point, I've always found the hacksaw to give a much better cut. I'm not concerned about speed in the slightest.

Clive Brown

Hafta disagree about the need for a damper in working order.

Ran mine for years with the damper in as purchased setting, assuming as it came out of as proper engineering shop it would have been about right, and wasn't greatly impressed as it didn't seem to do much in the way of blade lift on the return. Eventually it stopped doing anything at all.

Initially I assumed I'd just pushed some of the oil out over the years when lifting the saw bow when some resistance could be felt. Fortunately I decided to investigate before refilling. Found the spring at the bottom adjusted to coil bound and the needle doing nothing so effectively the valve was more like a cork in a bottle than a damper. After some head scratching I figured out how it should all go. Set the spring to a moderately low tension so the plate could move, guessed at a sensible tilt setting for the plate and filled it with ISO 32.

It now does what it should giving a nice force reduction on the blade on the return stroke. Clearly it never been in working order in my ownership before.

Clive

Hi Clive, i accept that a damper is nice to have, it should improve blade life by avoiding load on the blade during the return stroke. Without it my blade bears full weight on the workpiece on both forward and return strokes. The forward stroke cuts as it should. However, for my limited use, blade life seems good and the saw has done what I need. Marcus's description is interesting but I don't think now that I'll ever get round to fitting a damper.

Must admit, I quite fancy a Chinese bandsaw instead of the massive old donkey!

Clive

Chris,

You could do worse than buy one of those Cheapy Crappy Chinese bandsaws !

I bought one some twenty years ago and it,s still working away, I have cut everything from inch x one eighth up to six x four RSJ and everything in between. At this stage it owes me nothing and will no doubt see me out. Needless to say, the hacksaw has an easy life these days.

Do yourself a favour and get one.

Well, thanks again to Marcus. I've now reinstated the damper and stop mechanism. Interestingly mine is M6 not ¼whit, I wonder if yours has been redrilled/tapped at some point, or perhaps an older model. Luckily I had some M6 rod in stock, so no drama. Just waiting on new blades now. What's your preference? I've gone for 10tpi as the middle of the road option, should do everything well enough?

All the best

J

Well, thanks again to Marcus. I've now reinstated the damper and stop mechanism. Interestingly mine is M6 not ¼whit, I wonder if yours has been redrilled/tapped at some point, or perhaps an older model. Luckily I had some M6 rod in stock, so no drama. Just waiting on new blades now. What's your preference? I've gone for 10tpi as the middle of the road option, should do everything well enough?

All the best

J

J

I'm glad you managed to get the damper sorted.

The spec of the saw blade varies a bit depending on what you are cutting. For steel, and most other metals, I use 10TPI (Eclipse All Hard blade). For plastic, I use 6TPI which can need a bit of care when starting the cut, and is not suitable for small diameter bars. That's a Starret because the technical people there gave me good advice on number of teeth etc. 6TPI is useful for aluminium blocks too, but for both plastic and aluminium the blade must be very sharp. I have used 7TPI too, instead of 6TPI. The big advantage of the 6TPI is that it clears the chips and cuts sufficiently fast that the plastic doesn't melt with the friction and grab the blade. I had that trouble a lot with large diameter bars of plastic, before I changed from 10 to 6TPI.

As for the Whitworth thread, I suspect my saw is much older.

I notice that the cast arm on the main casting which operates the damper had been repaired (quite badly) before I got the saw. Because my damper cylinder has a groove running down the inside, the damper is not effective, and the force of the balde assembly coming down a bit too hard over a long time and lots of cuts has now severed the arm once more, leaving me a tricky repair job <sigh>. Having said that, I wouldn't want to part with the saw, as it does a really good job, if a little slowly at times.

Marcus