Author Topic: Modifying my power hacksaw  (Read 4937 times)


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Modifying my power hacksaw
« on: July 01, 2009, 04:32:35 PM »
At last I am starting to get thru my projects backlog pile.

Today, it happened to be the power hacksaw that got it.

I have a modern day Chinese made power hacksaw, a fine machine that does the job. Unfortunately it has one slight fault.
They have fitted an air strut that helps you lift the weight of the saw arm at the end of the cut, or when you need to mount new material to be cut. The problem being, this also supports the weight of the arm all the time, and only allows a slight pressure onto the blade, so it would take an age to cut thru even a small piece of bar. I have been getting around the problem by putting weights onto the lift handle, so putting pressure onto the blade to make it cut more efficiently.

So now to the fix.

A little while ago, I chopped up a perfectly good 24" high, super accurate height gauge. It had to be done, it was offered around and no one was willing to take it off my hands, and on the open market, it just wasn't worth the time and effort to advertise it for sale. This 'recycle' job left me with a good micrometer head, 24 perfect 1" super hard ball bearings, and a load of metal that is very difficult to machine, so really worth nothing.

Then came the problem with the saw, and I needed a good solid heavy weight, and a bar to hang it on.

The base for the height gauge was perfect, as was the tube that held the balls, it just needed a bit of machining.

I am a great believer that if I modify a machine, it is done in such a way that the machine can be reverted back to as near it's original state as possible.
I took a bit of Ralph's garage door operating lever, and made a strong point on top of the saw, to take the stresses of the arm and pressure weight, it was fixed to the top of the machine using original mounting holes.
The next bit was the part that made Stew do his song and dance routine. I was turning 6mm off the diameter of the hi tensile tube in one hit, so that it would pass smoothly thru the hole in the weight. The slot along the back of the tube was already in there, it was that which made all the seperate hot chips that flew everywhere, by making it an interupted cut.
Along the strong point plate, I machined a half round slot, not big enough to take the bar, but enough depth on it told hold the bar in position once it was bolted down.
The weight had a grub screw hole that penetrated into the main hole. I stuck a cap screw into it that penetrated thru and sat in the slot of the tube. This allowed the weight to slide up and down the tube, but not swing side to side.

This is the side view. As you can see, the weight can be slid along the tube to allow the pressure to be adjusted for the material being cut.

Saw in action, happily recycling a bit more garage metal into useable lengths.

While trying it out, I noticed the weight was 'walking' towards the handle. A half hour job tomorrow will have an adjustable stop in place, which will cure the problem.

Never waste anything if you can help it. This time it finished up as perfect material for the job. Height gauge to counter weight in one easy lesson.


Offline John Hill

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Re: Modifying my power hacksaw
« Reply #1 on: July 03, 2009, 09:24:33 PM »
Good work there Bogs but I do wonder why you didnt just take the gas strut off?  Or maybe even moved the strut pivot so that below 'X' degrees the strut would exert a force downwards? :scratch:
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Re: Modifying my power hacksaw
« Reply #2 on: July 03, 2009, 10:54:11 PM »
A very good point there John, and a thing I did consider doing.

Really the strut has to be left on there, to assist you into getting the bow into the locked up position.

Rather than playing about with the pivot points, I just went for the easy solution. The saw has to cope over a large angle range, and the method I have used is an age old one when dealing with these power hacksaws.

Some use a slowly collapsing hydraulic strut, and is set for pressure by an adjustable bleed valve, others use the sliding weight method.