power hacksaws mechanisms/hydraulics

[Scruffy]

I have 2 power hacksaws. Don't bother with the adjustable stroke. Just move the vise or put a block behind the material being cut.
If you keep everything clamped securely a blade will last a year.
Thanks scruffy ron

 

[ecosta]

Hi Ron,

Thanks for the advise and for taking the time to answer.

Regards,

 

[projectnut]

Are you in need of a power hacksaw, or a project? If you just need a saw you can probably purchase a commercially made one for less than it will cost to buy the materials to build one. I was considering building one a couple years ago. Then I ran across a Racine 66-W2 saw for less than $200.00. All it needed was a good cleaning and some new blades. There are currently several available on eBay. They range in size from mechanical ones that will sit on a bench top to monsters that will fill a room. Prices are also all over the board. There's a Keller 36" machine with a starting bid of $99.00, There's another smaller Keller and an Excel machine in the $200.00 range.

Here's one that was for sale on another bulletin board a couple years ago. It's almost identical to the one I bought. Note the selling price was $75.00.
http://www.practicalmachinist.com/v...ory/racine-utility-power-hacksaw-sale-305652/

 

[brino]

Interesting thread.
A couple comments.......

Like I said earlier, it is actually a very simple system! Let me know what you guys think.

Hi Terry, you gave a great list of features/requirement, but one thing I didn't see you mention is that there is also some careful timing between blade stroke and pump stroke, such that the blade lift happens on the blade return stroke.

I have a Kasto power hacksaw, it uses a hydraulic feed system. The cylinder is at the rear of the saw, further back from the pivot point, so as the cylinder extends, the saw blade goes down. The cylinder I'd single acting, hydraulic pressure to extend and a spring inside the rod end of the cylinder to retract the cylinder, and lift the blade.

Hi David, thanks for the description of your saw. I have not seen one like that, but I like that if the hydraulics fail then the blade will be lifted out of the work. That could be a great "fail-safe".

If I got David right, even Kasto uses negative pressure

@ecosta, I suspect they don't. Most oil hydraulic systems use positive pressure, from car brakes, log splitters, tractor loaders and automatic transmissions.
The only place I have seen negative pressure systems was with air vacuum systems used on Audi door locks, 4-wheel drive front axle disconnects, and other light duty stuff.

-brino

 

[Bob Korves]

@ecosta, I suspect they don't. Most oil hydraulic systems use positive pressure, from car brakes, log splitters, tractor loaders and automatic transmissions.
The only place I have seen negative pressure systems was with air vacuum systems used on Audi door locks, 4-wheel drive front axle disconnects, and other light duty stuff.

Negative pressure in hydraulic systems tends to get air in the system, leading to sponginess and poor performance.

 

[Chipper5783]

Negative pressure in hydraulic systems tends to get air in the system, leading to sponginess and poor performance.

I think Bob is right. I don't think the Kasto has a negative pressure in the feed cylinder at any point in the cycle. It uses a single acting cylinder (pressure on the cap end, only atmospheric pressure in the rod end). There is a very substantial spring in the rod end, so when the small retractor pump allows a little oil out of the cap end of the cylinder, the force that develops the pressure to cause the oil to flow out to the retractor pump is from the spring inside the rod end of the cylinder. I'd be very surprised if the pressure ever went below atmospheric.

As Bob pointed out, negative pressure would not work very well. My experience with this saw is that the feed works well (which it should, back in the day this was not a cheap saw).

 

[Terrywerm]

Hi Terry, you gave a great list of features/requirement, but one thing I didn't see you mention is that there is also some careful timing between blade stroke and pump stroke, such that the blade lift happens on the blade return stroke.

You are correct, it was not mentioned, but the timing would be as simple as a cam or eccentric on the crankshaft. My Keller saw already has one for the ratchet and pawl lift that the saw currently has. The ratchet and pawl system works fine if everything is tight, such as on a new saw. Once the usual wear comes into play, the system takes less and less pressure off of the blade during the return stroke.

 

[magicniner]

If the blade cuts on the forward stroke and is set so that it lifts the arm as it moves forward all you need is a hydraulic cylinder with a one way valve in the piston allowing lift and an adjustable bleed valve to allow the blade drop speed to be set.
That's how the Rapidor Manchester power hacksaw works.
The Rapidor also has multiple points at which the fixed vice jaw can be set, allowing the saw to be set up for various work sizes but also allowing the use of the unworn sections of blade if you only cut small work.

- Nick