Details for a scroll saw

I want to make a scroll saw for thin metals, grp sheet, ply & balsa ( model aero building).

I would appreciate comments on the following:-

1) How many oscillations per minute do forumites reckon I need. I will have a simple eccentric & the number of revolutions will govern the number of times the blade goes up & down.

2) How far up & down would you reckon the blade should travel. This will govern the size of eccentric. is 20mm enough or too much? Should it be faster & less stroke length or slower & a longer cut. Presumably the upper spring will have to adjust to this & thus govern the stroke. But it must affect operation somehow

3) I seem to recall a standard single phase motor of about 0.25 HP runs at 1450 RPM. Is that correct? & any ideas where I can source one cheap?

4) I will cut the gears from tufnol as I have only just bought the lathe & mill ( Promised delivery Friday-- Hurrah!!!) so I want to go easy on the cutters.

So how big should the teeth be. I know the ratio is set by number of teeth to number of teeth but should I be looking at very small teeth. How does one decide on tooth size on gears . Is there a table somewhere that one follows. Would smaller teeth be better on tufnol ? Bigger may be easier/ quicker but will the tooth snap off? should I have small teeth for quieter running or will they just strip off?. Or is it decided by the divisions available on the dividing head?

Finally - No; I do not want to buy one. Half the fun is making it ones self

Thanks

1000-1500 strokes would be about right so could come straight offa 1450rpm motor and save having to make gears.

15-20mm stroke is usual.

Use sheet tufnol not rod

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... and, it should be one of the fabric grades, not paper.

MichaelG.

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Edit: There is a very useful document linked in my post on this previous thread..

... Ooops: the link to Tufnol's document is dead 

... But this should suffice.

Edited By Michael Gilligan on 26/01/2016 19:21:44

Glass fibre is brutal on teeth, choose cheap bladed for this, Thin metal will require really fine teeth 60 TPI?, wood can be a lot more coarse 20 TPI. I saw a man cutting out wooden jig saw in a booth at the sea side. fascinating, the blade was very thin and narrow, consisted of 4 teeth in one direction then 4 teeth in the opposite direction followed by a space equivalent to the series of teeth, then another series of teeth. So it cut on the up and down motion. quite slowly, 2 strokes/sec?

Speed of motor is related to its construction (number of coils) and not its power. 1450 is a 4 pole motor, about 2900 is a cheaper 2 pole motor.

I some times mount a switched on jigsaw under a modified stool, so the blades pokes up where the seat would be. So its a bit like a fret saw with a thick black. I think this is the easiest way to go, do this with a spring loaded top support for your blade and you can be away in a day or so.

Frank

Actually I had thought about that. I have 4 or 5 jigsaws from my joinery business & had considered just making a blade grip. & doing exactly what you suggest. The variable speeds would enable me to experiment.to get best cutting speed. I already have a startright bandsaw

I just fancied trying some gear cutting & making the eccentric

Edited By Sam Longley 1 on 26/01/2016 20:42:33

Sam

Check out the design used for the Emco Unimat SL jig saw, you have a lathe so just follow the SL design and build it to suit your machine, you won't need to worry about cutting gears as you have different speeds available on the lathe spindle. If you need pictures and dimensions of the SLdesign just ask.

Emgee

Not sure a stool is the best place for an upside down jigsaw, some of us are getting on a bit, could forget and sit down, probably jump up quicker too if a bit younger.

If you look at old copies of "Popular Mechanics" there are a number of scroll saw designs, some dating to before WW2, there are 3 in the PM book "Forty Power Tools You Can Make" published in 1941/42/44, you would find them on the PM web site.

Ian S C ps, I have a home made scroll saw that I got at a church fair, about the only metal is the table, the arms are wooden, as are the pulleys.

Judging by the types of items you envisage sawing, I'd go for a scroll saw that uses piercing saw blades. I do a lot of piercing in my work as a jeweller, and I once purchased a Hegner scroll saw for the purpose. The good points were the Hegner reputation and the fact that it accepted piercing saw blades.

It was OK in most respects except it was too fast (60-110 strokes/min is ideal for piercing blades) and the stroke was nowhere enough to use the full length of a blade. A minimum stroke of 50mm (70 would be better if its adjustable) is required otherwise the blade is worn out over just a short section. I had the Hegner rep come to see the problem and the agreed that it wasn't suitable and accepted it back. Pity, 'cos it was a nice saw; just no good for piercing blades,

Here my take on this for what its worth.

1. The bigger the stroke the better. You buy the whole blade so use it.

2. Much lower speeds for metal than wood so ensure you have a good low speed range.

3. Engineer in a vacuum extract nozzle to clear the dust so you can see and for fibreglass material you don't inhale the stuff.

4. Maybe a fitting for a suitable magnifier.

5. CNC controlled material feed. (optional)

regards Martin

This is worth a look

**LINK**

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It sure is

Thanks

MichaelG.

Gary, same problem with jig saws cutting sheet steel, about 20mm blunt 30mm unused. Next time, sit the jigsaw on a 22mm bit of chip board sitting on the steel to be cut. You can now blunt the next 20mm.

Frank

Sam,

Have sent you a PM re suitable motor

Phil