Rapidor Manchester Damper

[nigel jones 5Participant @nigeljones5]

[nigel jones 5Participant @nigeljones5]

Just bought this saw to cut copper tube up to 6" diameter. I need a very light feed weight or it will simply tear at the copper and bend it. There is a damper of sorts, A metal ball inside a tube which I assume should sit in oil? There is a sprung plate on the bottom of the ball that I assume alters the damping rate but the ball is not a good fit inside the tube so oil comes past it regardless. There doesnt seem to be wear on the ball part its just not a great fit – should there be a seal on it? Thanks

[Nick HulmeParticipant @nickhulme30114]

The piston has a spherical surface and the hole in the top plate is a slot because the angle of the shaft to the cylinder varies with blade height, no seal I'm afraid.

The plate is the valve.

I'm currently running mine with very gloopy straight STP additive but it is my intention to bore and hone the cylinder and machine a plastic piston, but I've been using it for 15 years and it hasn't actually failed per se as yet 😀

– Nick

[Clive Brown 1Participant @clivebrown1]

Not sure that the damper will really do what you wish. Its basic purpose is to keep the bow slightly raised on the return stroke, to reduce blade wear, after the bow has been slightly lifted on the cutting stroke. This lift comes about due to the saw geometry, the blade is not quite parallel to the guides. Hence the work-piece will feel most, if not all of the bow weight at some point on the cutting stroke. The damper will not take very much at all irrespective of the oil or the valve adjustment.

Edited By Clive Brown 1 on 01/11/2017 19:31:43

[Nick HulmeParticipant @nickhulme30114]

Clive,
Fizzy has the right idea, when the damper is fully functional it can be used to control the drop speed of the blade into delicate parts and the drop can be set so slow that when started above the work the blade will never lift, just taking a very small cut at each forward stroke,
Regards,
Nick

[Clive Brown 1Participant @clivebrown1]

Nick,

OK, must say that the damper on my elderly Rapidor was never really very good and I eventually discarded it, but I didn't see it as being able to take much weight on the cutting stroke.

If Fizzy gets his to do as you describe then that's a good result..

Clive

[Nick HulmeParticipant @nickhulme30114]

Clive,
The damper has a valve disc allowing free lift but adjustable damped fall, if I turn the fall speed down I can reduce it to pretty much static, it takes my weight.

Once the blade engages the work the damper will not be taking weight on the cutting stroke as the blade mounting geometry lifts the arm on the (forward) cutting stroke, for delicate material you would be relying on the damper feed lowering the blade slowly enough that the depth of cut was small enough not to damage the material,

– NIck

[Mike PooleParticipant @mikepoole82104]

For cutting copper tube I think you should be looking at fitting a fine tooth blade but you may not find any finer than about 14tpi which using the 2-3 teeth in contact means a wall thickness of near 6mm, the Rapidor is a good saw but a bandsaw with a fine blade may be better for tube. Using the damper to control the cut is probably a bit optimistic even if it is in A1 working order. I bought my Rapidor to save me time but I just love watching it work, it does save me breaking into a sweat though.

Mike

[LambtonParticipant @lambton]

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Eric

[BazyleParticipant @bazyle]

The thing to do might be to arrange a lever out the back to exactly counterbalance the saw. Then arrange a wire over pulley to weight system to apply a cutting force that does not vary with angle. during the progress of the cut. This works better for bandsaws as the movement of the blade frame adds a complication.
After further thought how about a roller rest out the front that the blade runs on (hopefully hard ballrace bearing resists being cut) and a ratchet driven screw thread height adjustment on every stroke, bit like a shaper adjusting it's cut.

[nigel jones 5Participant @nigeljones5]

Thanks everyone…lots to think about

[Nick HulmeParticipant @nickhulme30114]

Posted by Bazyle on 02/11/2017 09:14:50:

The thing to do might be to arrange a lever out the back to exactly counterbalance the saw.

I love that idea, adding weight to a Rapidor

[Martin KyteParticipant @martinkyte99762]

All the commercial use mechanical hacksaws I have ever seen have had weight added to them on the bow to increse the pressure on the blade. !

regards Martin

[Clive FosterParticipant @clivefoster55965]

When cutting thin tube on my Rapidor I usually push something into the middle to provide more support for the blade. Usually a lump of wood that happens to be to hand and wedges adequately in place after a rough shave of the corners. Inch thick vertically is usually enough to be stable and provide sufficient extra support.

As fizzy uses a restricted range of tube sizes making up a length of cruciform filler for each size by screwing or nailing suitable bits together would probably be worth the effort. Loose about half an inch for each cut so a foot or two would last a while.

The Rapidor I use has the fixed right angle cut vice holding the work on both sides of the cut. Seems to be more stable with thinner material than the overhung, angle adjustable, version. If fizzy does mostly right angle cuts with an overhung, adjustable, vice it might be worth looking into adding extra support outward of the cut.

Bottom line with a Rapidor is that it follows the Stonehenge design philosophy. Simple, effective, just on the right side of crude, long lived and darn hard to break. Subtle it isn't.

Martin

Cheapskate owners figure weight is cheaper than new blades.  Makes surprisingly little difference to cut times unless huge.

Clive.

Edited By Clive Foster on 02/11/2017 11:01:50

[Nick HulmeParticipant @nickhulme30114]

Posted by Martin Kyte on 02/11/2017 10:50:14:

All the commercial use mechanical hacksaws I have ever seen have had weight added to them on the bow to increse the pressure on the blade. !

regards Martin

Martin,
The Rapidor was supplied with a weight for the bow, I was referring to the user adding non-design weight, specifically hanging out the back to counter-balance the moving weight of the bow as suggested 😀

– Nick

[Phil WhitleyParticipant @philwhitley94135]

OK, heres a question for all you Rapidor users (I have one too!( which way should the rotation of the flywheel be, and which way round do the blades teeth go, does it cut on the forward stroke, or the back stroke? My rapidor works well, but Every time I ask I get different answers!

Phil

[Clive FosterParticipant @clivefoster55965]

Phil

General rule with power hacksaws is that they cut towards the fixed jaw of the vice. On a Rapidor that will be the forward stroke so the teeth should point forward. If I look closely at mine its just possible to see the dashpot / damper assembly lifting on the return stroke.

Flywheel direction of rotation is good question. Mine runs clockwise when looking directly at it so the forward stroke comes as the crank goes over the top. Running anticlockwise the forward stroke would be when the crank swings underneath so there is some difference in crank geometry. Thats the way it was set-up in the workshop I got it from so I figured it worked.

Given that the blade lift on the return is said to be due to the relative geometry of pivot and bow guides its possible that the difference between over and under on the crank has some effect on cutting pressure. A question best left to those with serious understanding go such geometries.

Clive.

[Phil WhitleyParticipant @philwhitley94135]

Thanks Clive, that is how mine is set up at the moment. The confusion started when someone (who is "in engineering&quot told me it should have the blade in backwards, ie teeth facing the rear, and then I thought about it, and realised that as mine is three phase, and I cannot find any arrows for direction, it may be wrong! I will leave it as is for the moment, because the workshop is all in a heap because I am re-laying the concrete floor in the main part of the shop (6mx9m) Actually, I will just be the readymix labourer. ^the lads^ will be doing the clever stuff! When it is done and finished, I will take of the belt guard and have a look at the pulleys.

[nigel jones 5Participant @nigeljones5]

Just realised mine has no packing between the runner arms so it is impossible to set up correctly. Does anyone know what form the packing should take?

[Clive Brown 1Participant @clivebrown1]

The packing on mine was cut from thin wood, probably about 3/16" thick. 4 pieces in all. Basically a rectangle with a slot for the bolt and a curve to follow the outline of the cast runner plates. I made a replacement from plywood. Anything slightly squishy would probably do.

Edited By Clive Brown 1 on 05/11/2017 10:54:58

[nigel jones 5Participant @nigeljones5]

thanks all, got it running as true as it is likely to be given its age, the idea of a support for the overhang or even another vice seems like an excellent idea. Still looking for a fine feed damper, thinking of a bottle jack?

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