The need for speed

[StevieB]

Following on from the treadle powered saw in the general topic forum, I got to wondering about blade speed. Although treadle powered saws are geared (large wheel to small reciprocating wheel) I presume the actual blade speed is both not high in terms of stroke per minute and not constant since its human powered.

Simple question then is - does having a higher or lower speed make for more accurate cutting, which is best? I know Gill says she cuts at a relatively low speed compared to other scrollers, personally I use about half speed for reasons of both control and vibration issues on my saw.

Are different speeds required for different applications - thick timber, compound cutting, stack cutting, delicate work? Or do you simply whack the saw on at max and go at it :wink:

Steve.

 

[JackL]

I used to have a treadle powered fret saw and constantly had problems with variations in speed changing due to the fact (a bit like patting your head and rubbing your tummy) that I couldn't concentrate on the cut and maintain a constant speed on the treadle :roll:
I now use the slowest speed only on my powered scroll saw. In fact, I've never actually sawed with it on the high speed. (Am I missing out on something here?)

 

[Gill]

I don't know if speed affects the accuracy of cuts. Blade tension and the type of blade is probably more important in this respect. If you get a blade with too much bias (yes, Mr Blade Manufacturer, sometimes batches of poor quality blades manage to sneak out of your factory) and then fail to tension it as tightly as it needs, you'll find the blade wanders off on a frolic of its own.

Furthermore, some woods with strong grain can divert a blade from its course. Generally speaking, though, I find this is something which I can anticipate and adjust the rate at which I feed my workpiece in to compensate.

I find there seems to be a relationship between the speed at which you feed the workpiece, the stroke speed, the nature and thickness of the wood and the type of blade. It's not really possible to identify a formula for success with so many variables. If there's one maxim that governs my approach, though, it's "let the saw do the work, let the blade do the cutting". I always aim to get the maximum swarf removal because this will keep the blade operating at its most effective. Blades need time to disperse the swarf at the point of cut! It's certainly possible to have the blade going hell for leather cutting a woolly piece of soft pine and make slower progress than you would gently cutting a piece of ash.

How do I decide what speed to use? As I said, there's a variety of factors to consider so perhaps it's more useful to try to establish when I reckon I've got too fast a speed. One sign is that fine boards (and, for that matter, blades) break. Another is that the blades seem to get blunt more quickly than I'd anticipate. I've seen it said elsewhere that a blade should last 15 to 20 minutes. Not in my book! That might be true when cutting certain projects but often you can extend the life of a blade considerably just by slowing the machine. If you don't believe me, try cutting something with a handframe fretsaw and see just how effective these saws are. You can cut quickly and the blades seem to last much longer because less heat is generated through high speed cutting. Sometimes I wonder if the only real reason to use a mechanised saw is that it will give you a consistently square edge (and it won't tire you out ).

In my book, a faster cut means more friction and more friction means more heat. More heat means that blades lose their cutting edge more quickly. I try to cut as slowly as possible.

Gill

 

[StevieB]

Sounds like its a case of experience and trial and error then! The reason for asking is that I am still having issues with compound cutting accurately. Squaring the table to the blade has definately made it better after some adjustment to the tilt mechanism with a small file but I am still getting a slight drag on the blade resulting in the bottom of the blade not cutting the same line as the top of the blade. Was wondering if this was related to speed of cut.

From Gills answer I would guess possibly, but in relation to swarf clearage and possibly a too high a feed rate than too fast a blade speed. I still have a few blades to try (my workshop time is sooo limited at the moment the spiders dont recognise me!) so will persevere.

There are some compound ornaments in this issue of Scrollsaw woodworking and crafts I might have a play with as they seem to be a more simple shapes than the chess pieces I have been trying so far - might be a case of trying to run before I can walk I think!

Oh, and for anyone who gets that mag I have, for the first time ever, spotted the fox!

Steve.

 

[Gill]

Sounds like its a case of experience and trial and error then!

It probably is :roll: !

Remind us, Steve - what saw are you using? I take it from your description that the inaccuracy is back-and-forth rather than sideways? If it was sideways, I'd definitely suggest the most likely cause would be a table that wasn't square with the blade. The easiest way to check this is to take a square block of wood, make a slight cut, then try to fit your blade into that cut feeding the wood in from behind the blade. However, if it's back and forth, it would be worth experimenting with a different type of blade. Go as large as you dare and try a skip tooth. No doubt I'll need to find my tin helmet, but if that doesn't sort it out, I suggest you use a scroll reverse blade and see if the agitation from the reverse teeth helps to clear the sawdust. I find SRs can be surprisingly effective.

Oh, and for anyone who gets that mag I have, for the first time ever, spotted the fox!

I haven't got my copy yet - it's not fair and I'm going to sulk [-( .

Right, sulk over . Do you subscribe direct to Fox Chapel, Steve, or through GMC? My subscription is with GMC and I'm wondering if it makes a difference.

Gill

 

[StevieB]

In this instance the saw I am using is the Axminster AWFS18. The table was indeed out of square with the blade using the cut a block and put it behind the blade method by about a sixteenth of an inch. This I have fixed. The drag I am referring to is front to back, almost as if when I feed the timber into the blade the top cuts to the line but the bottom lags slightly behind. When you turn a corner this results in a skew when compound cutting with the result that the entire piece looks twisted. To explain this better - if you cut a thick piece of timber straight through, the blade should exit the timber vertically. I find that the top of the blade is exiting first, then the bottom. The line itself is vertical so cutting straight lines is fine. Its curves or changes in direction that are the problem. I think as you say better swarf clearance with a larger blade is the answer - just need time to have a play.

Regarding the mag, I subscribed direct with fox chapel - sent off for a free trial issue then subscribed direct for 8 issues (2 years) with the card that came with it. This issue only came yesterday so I doubt yours is far behind!

Many thanks for the advice,

Steve.