Hmmm not sure but have to agree that Dave really is a nice chap. Cant wait to see the final product. Nice to know its finally going to get some use. Good luck.

Cheers

Dave

Unlike Johns Axminster device the little Kennedy power hacksaws work just fine with a damper. The Kennedy takes a standard hacksaw blade and is probably around the same effective size as the Blackgates machine.

As I remember things correctly from a quarter of a century (ish) back the Kennedy in the departmental support workshop had a damper dashpot about 2" diameter with a fairly loose fitting "piston" effectively comprising a pair of thick washers with a couple or three large holes drilled in them. The amount of damping was adjustable via an L shaped rod sticking up through the middle which rotated one "washer" with respect to the other so altering the amount of free oil passage through the piston. About 1/3rd of a turn adjustment covering a range sufficient to let the beast cut adequately fast on solid bar yet be reasonably under control when dealing with reasonably thick wall tube. Waterpipe and the like. Very thin wall tube, such as Speedframe, was a bit too much for it. I imagine there was some sort of flap valve included so that the oil didn't get spalshed out when the unsympathetic hoiked the arm up rapidly. There was still noticeable drag when lifting. When the beast was running a certain nodding of the carrier arm could be seen. Probably not enough to indicate actual lift but certainly suggesting a reduction in blade down pressure on the back stroke. Some sort of geometrical magic going on.

Allegedly oil specification is important but ours seemed to work just fine getting a splash of whatever was handy when I noticed things getting low. No one else cared and the place wasn't exactly a regular haunt so for much of the time the oil level would ahve been wrong. Dashpot seems to have been a refinement rather than necessity as the saw still worked pretty well with it near empty. Decent write up on http://www.lathes.co.uk whith probably enough detail in the pictures for you to scale off.

Clive

Clive,

Well done, nearly remembered it right after 25 years!

The first "washer" you mention is in fact the piston, about 1/4" thick, with the holes in it. The second one is a thin disc (shim thickness) which can move up and down to either cover the holes or uncover them and let oil pass round it in the lifting position. Adjustment as you say, by a rod, threaded at bottom, which can vary the distance between piston and shim.

The only thing that stops the oil coming out of the top is a rubber boot, such as on car steering arms.

The makers specified the dashpot oil as "the special Wakefield Cresta V oil" (which was supplied). Though any reasonably thick oil will do.

There was a very strong pull down spring on the machine, the dashpot smoothed out the action.

Phil

As I'm having a "shaky" episode, therefore fit for not much, I got out a Kennedy that has no oil in the pot and took a few pics of the dashpot to illustrate what Clive and I are talking about.

They are in an album "Kennedy Dashpot" here **LINK**

Note the gaiter is not the proper one, and doesn't work very well. The proper one is a concertina type.

Note also the curved sides of the piston. This allows the angle of the piston rod to change as the arm goes up and down without the piston binding in the pot.

The pot is 1¼" dia. and 3¼" deep.

Phil

PS  The creator of the album "Jo Robinson" is the Missus, not my alter ego.

Edited By Robbo on 26/04/2014 15:33:24

Although you can get away without a damper on these small hacksaw machines if you only cut solid material of a certain range of sizes, probably covering a couple of inches, around the sweet spot where downforce weight and blade tip co-operate to give best cutting you will run into trouble with tubes and material significantly outside that range.  With the aforementioned departmental Kennedy the usual sign that it needed a dashpot top up and, probably, a quick survice was a blade jam or breakage when cutting thin material. Usually the speedframe 1" square tube construction system which we used a lot of. Correct setting of the damper also made a big difference as to squareness of cut. For solid bar, especially at the larger end of the machines capacity, minimal damping was needed for a reasonable rate of cut. In thin materials and speedframe minimal damping resulted in a very unsquare cut but with the damping set appropriately a decently square end was produced.

Ordinary hacksaw blades aren't really stiff enough for power machines. Best blades we found were Keranous(?) Progressive Teeth type which could be got in a thicker (double?) than normal version as well as standard type. The extra stiffness gave noticably better results and the progressive teeth faster cutting. Gawd knows when the stash was got but when it was gone replacement proved impossible as the firm had disappeared. The dashpot also seems to reduce the pressure on the blade during the return stroke leading to longer life.

The Axminster style gas spring to control down force is just plain wrong and needing to add weights plain silly. Its arguable that a machine with a sliding weight on the arm with its position calibrated for different materials, thicknesses et al could be nicely engineered to both work well and be inexpensive to produce but for a firm of Axminsters size to supply a machine that doesn't work out of the box is plain daft.

Our Kennedy never had a cover over the dashpot in my time but I suspect the last few bits dropping into the cavity where what jammed up the dashpot giving me the opportunity to find out what was inside.

Clive

Edited By Clive Foster on 27/04/2014 11:53:17

Interesting observations on damping. My badsaw slows to a sudden and complete halt on cast iron if the cut is more than 2" long. 8" of 2" square MS balanced on the end got things moving again. It has no such problem with steel and blade is sharp. In contrast, cutting a 3/4" steel tube the other day as soon as it was past the top 'whoosh' to half way through and threw the blade. Would have been quicker to use the hacksaw :-/

So my thought at the moment is some combination of a damper and a weight.

Neil

Neil

the issue you hah may be not enough teeth on the blade in contact with the work. On the top lots of contact then suddenly you're only cutting wall . You really need about 3 teeth cutting at any one time. I have issues cutting tube and you just stick a bung in it of wood and cut through the lot. There's lots of explanations why in various books but filling / bunging it works most of the time.

Regards Ian

Graham.

I've had one of these hacksaw's for a number of years & it's served me very well ( I get no fun from using a hand hacksaw!!)

A few improvements I made to mine are :-

1. I fitted a second bar parallel to the existing slide bar which helped in stopping the blade running off.

2. Fitted flip top oilers to the slide bar & shafts.

3. Secured the vice feed screw in the moving jaw so the jaw moves in or out when the screw is turned

4. Adding a weight to the handle improves the cutting.

Mine is mounted on a box with the motor enclosed underneath for the only reason that the motor is rather large ( It's the only one I had at the time) I must keep a look out for a smaller one. The whole lot is mounted on a shelf fitted with runners so it can be slid into the cabinet when not in use.

Ian

A few photo's showing how the out rigger bar is fitted,