Power Hacksaw

Heko Junior Power Hacksaw

I purchased this Heko saw on ebay. It takes 12" x 1" (or 1/2") saw blades. To provide down force on the saw blade it uses spring tension. The saw was originally manufactured by a family business, in Dunkeld, Victoria, Australia - for small business & farm maintenance work. It was mostly built using stock steel sections with a minimum of castings (flywheel) and forgings (vice handle, saw bow). It was made to be light, sturdy, simple, effective and affordable.

When purchased, mine was missing the motor (originally 1/3hp), pulley, belts & blade tensioner. There was, as you'd expect, a moderate degree of wear. It was in quite good condition for its age, probably about 40 to 50yrs old. I obtained an old 1/3hp motor several months back, I put it to use here.

I found it ran a bit fast for harder metals, so I made a lay-shaft to slow it down - See lower down the page.

	Side view showing the flywheel (which the original twin vee-belts ran on), the saw frame & the lifting arm.
	The other side, showing the motor mounting plate & the vice.
	The 'working' parts of the saw. The reverse of the flywheel shows the eccentric which moves the sliding frame back & forth.

Wear can be seen at three points marked with X's on the sliding mechanism. On the flywheel, wear is visible as a flat spot on the eccentric near the shaft hole & directly opposite to it. There is currently about 1/8" to 3/16" total of wear on the eccentric.

My lathe isn't large enough to swing the flywheel, so I machined the old eccentric off & bored the new bearing hole on the mill-drill.

Although it would have been fully functional as it was, I did the following:

	Repaired slider mechanism - milled contact surfaces until true & parallel. Installed four small ball races on hard steel shafts (both from old VCR's), shafts being brazed into place - for the slider to run on, reducing friction & wear.
	Repaired bars in contact with eccentric (responsible for moving saw backwards & forwards. Milled contact surfaces until true & parallel. Hard soldered brass wear strips onto the bars to compensate for the milled down (worn) surfaces.
	Milled off the aluminium eccentric, replaced with a 5" donut of 8mm aluminium, held into place with 8 countersunk machine screws about 16mm long (Secured with Loctite).
	Bored out 3/4" x 2" hole in flywheel, (it was originally un-bushed aluminium on a steel shaft). Installed two bronze bushes 3/4" x 7/8" x 7/8" - this left space of 1/4" in the hub centre, into which, drilled down through the hub, I put a grease nipple. The bearings were soaked in oil prior to pressing into place.
	Made double 'A' profile pulley for an old 1/3HP motor. Instead of using 2 vee-belts, I'm trying it with one Vee-belt. The belt appears to grip well on the flywheel without slippage. If the belt does slip in the future, I can just add a second belt. For the technique of making vee-belt pulleys see Die Filer page.
	A new motor mounting - the motor I am using is flange mount.
	A new blade tensioner was made.
	A power switch was installed on the motor mounting plate. A plastic box is mounted on the underside to protect the user from electrocution.
	I may convert it from spring tension down force on the blade, to a system using weights which can be added or removed. Until then, I have just made the spring tension adjustable.
	Re-painted, Assembled & lubricated.

Originally the shaft & sliding frame were meant to be greased with lithium grease & assembled. The grease nipple in the hub now means I just give a 'squirt' occasionally without disassembly. Meaning it's more likely to be done regularly & provide better lubrication, hence longer life.

Repairing / Rebuilding work done.

	New eccentric (blued for visibility), attached with 8 countersunk machine screws. Small amount of wear visible on the back of the flywheel, Ignored as performance will not be affected. Two 3/4"x 7/8"x1" bushings machined to 7/8" long, pressed in using the vice & soft cheeks, leaving a 1/4" gap in the middle as a reservoir, under the grease nipple.
	The new grease nipple installed in the hub. When the saw repair is completed, it will be re-painted.
	The sliding mechanism - worn surfaces milled down. Ball races visible on horizontal bars.
	The sliding mechanism in contact with the eccentric - worn surfaces milled down. Brass wear strips attached with hard solder. The new eccentric sits against these wear strips.
	The motor mountings are just simple strong shelf brackets. [ August 2007 - At the moment it runs at about 130 strokes per minute, but would prefer it to run at about 50 to 70 strokes per minute. I am putting a lay-shaft on it to give a further speed reduction. It's too fast for cutting hard steels at the moment & the blade gets really hot - more on this later - I have time to spare, but blades are expensive to replace.].
	Blade tensioner made from 3/8"x1" steel. One end drilled to take a small high tensile bolt (holds saw blade), other end machined down to 3/8" Dia & a thread cut with the lathe.
	I made the down-force tensioner easily adjustable by moving the mountings further apart & joining with chain.
	Finished & works like a dream - Pending the further speed reduction from the layshaft I'm making.

A Speed Reduction Layshaft is Added.

	I added a layshaft, as seen in the photo's. The drive pulleys are now 1.25" to 5", beside a 1.25", then to a 9.5" flywheel. This gives me about 65 strokes per minute (1440 rpm & 50Hz) - good for hard tool steels. The stroke length of the saw is only about 4.5", giving 293 inch/min cutting speed = 24.4 ft/min. Compare the modified drive to one of the above photo's.
	I used a salvaged pair of saddle blocks & bearings from an old evaporative air-conditioner. Made a shaft to fit, stopped it from moving laterally with set-screw collars. A long 1/8" keyway was made in one end of the shaft to drive the pulleys (one pulley was from an old compressor, the other, an old motor) - bushed, scotch keyed, machined to fit shaft. The keyway for the pulleys being cut on the lathe. Saddle blocks are mounted on a piece of 1/8" steel plate (record turntable base). A 4" door hinge had its loop bits (which go around the pin) welded a touch, so they can't splay open. The hinge was welded to the plate & bolted to the original motor plate. An adjusting bolt is fitted to the front of the plate to take up slack in the belt.
	Shown in detail from the rear - the belt tensioner bolt is just visible to the right of the left hand saddle block. Although you can't see it, the ball races are sitting in rubber mountings inside the saddle blocks. The two pulleys are separate units, simply mounted next to each other on the shaft. Job completed - working well.

Making a pulley for a Serpentine (Timing) belt.

Prior to having a dividing head or rotary table for use on the mill-drill, I chose to make the toothed pulley on my lathe (see photographs below). Indexing was done using my mandrel handle which is divided in degrees. Milling was done using an old GMC drill press modified as a Radial Drilling & Light Milling Attachment. As the milling cutter, I used an old broken twist drill. I reground it to approximate the tooth space. Of course, I only milled off a few thou at a time as this set up is not as rigid as a genuine mill-drill. The teeth were then lightly shaped & finished by hand.

	Machining the pulley - Old drill press doing light milling, indexed using the mandrel handle, pulley held on arbor between centres.
	Showing one tooth space to go - (wired) lathe dog visible behind pulley. Small broken drill, tip reground to act as end mill. The aluminium pulley was sleeved with a home made steel bush to reinforce the pulley.
Finished pulley for a Serpentine (toothed/timing) belt	Showing teeth, grub screw & bush. After milling, the pulley teeth were carefully filed by hand to approximate the involute curve on the tooth face. The whole pulley was then lightly polished with fine emery cloth.