Problems with curves?

[gasmansteve]

Hi Folks
Not really used my scrollsaw since buying it a while back so no proper scrolling experience. Started my wooden gear clock today and not happy with the spokes on the gears. I`m cutting 6mm ply with some Olsen 12tpi Reverse tooth blades but I can`t seem to get the nice curves I`ve seen on others work??. My Scheppeach decoflex has variable speed do I use it on max speed??.If I push very gently the blade doesn`t seem to cut so pushing harder the blade then seems to go where it wants. No doubt its my inexperience rather than the gear I`m using. Can the blade be too rigid?. I`m also not sure how small a radius I can cut with these blades.I`m ok with the actual teeth of the gears as I cut near the lines but finish off with my little 1" belt sander. Feel like chucking the ruddy thing out of the window :x Aaaah
Steve
Ps sorry got it off me chest now :wink:

 

[Gill]

When you first started talking about cutting a wooden gear clock, I never imagined it would be practically your first project! A little ambition is one thing, but...

It's a good idea to familiarise yourself with your tools and techniques by trying some simple projects first, or working through an exercise book such as John Nelson's Scrollsaw Workbook.

At 12 tpi, your blades are in the region of #7 or #9 sizes. I was cutting 35mm oak with a similar blade last night, so 6mm plywood should be no problem. Speed should make practically no difference with that blade and timber combination, although you will probably have greater control at slower speeds.

Cutting curves is not difficult but it requires practice. Beginners have a tendency to overcompensate when they veer off the pattern line, leading to a wavy effect. Be aware of this and instead of trying to follow the line at the point where the blade cuts the wood, look a little ahead (say 10 to 20mm) and aim to be on the pattern line at that point.

Can the blade be too rigid? No. It can be too slack though, even if it appears to be rigid. If you press against the blade from the side, you should have about 1 or 2mm of movement on a properly tensioned blade.

The blades should be able to cut quite a tight radius. Last night I tried to cut a radius which was a couple of mms and the blade binded, lifting the 35mm piece of oak off the table and whacking it down on my thumb. It hurt a lot. Yet I have negotiated similar curves before.

I think your problems with the blade not cutting, then seeming to veer off on its own path will disappear once you are more familiar with your saw. All blades have a slight bias to the right (it's the way they are made) but they should still be controllable. In fact, Olsen PGT blades are ground to minimise this bias.

Keep practising - you'll master it before too long .

 

[gasmansteve]

Thanks for that Gill
Thought I`d just be able to sit down and knock up a gear wheel :lol: little did I know..... Noted your suggestion of the blade having a 1-2mm movement well mine had a lot more than that guess I thought I`d overtighten it and snap the blade
and I also notice you do have more blade control going slower. BTW I know its like a piece of string but how long should a blade last?. I`ve been using the same 12tpi blade all day and not sure if its wearing out as I know people buy them by the gross is that because they break easily ?
Cheers
Steve

 

[Gill]

Hi Steve

Blade longevity will vary according to the thickness and type of workpiece, the blade size and the stroke speed of the saw. You can also extend longevity by covering your workpiece with low-tack masking tape because the substance used to coat the back of the tape acts as a lubricant. The big enemy of a blade is heat generated through friction. Scroll saw blades are very thin, so if you make turns that are too tight and scorch the wood the blade will heat up very quickly and the cutting edge will dull. It's the same if you try to feed the workpiece too quickly or if you allow dust to clog up the teeth (which is why skip tooth blades are so useful for cutting thicker timbers, counter-intuitive as it may seem).

If you let your blade do the cutting without any pressure from you, it will last longer. It's such an obvious thing to say, but in practice the temptation to feed your workpiece using pressure can sometimes be irresistible. As a blade begins to dull you will notice that feeding the workpiece does seem to take more pressure. This is a sure sign that the blade will soon need to be replaced.

It seems to be commonly accepted that twenty minutes is roughly the life expectancy of a scroll saw blade, although as I said before, there are many factors which can affect this. If you get a whole day's use out of one blade before it begins to dull, you are very fortunate indeed .

 

[big soft moose]

this could be a stupid idea so feel free to ignore me , but if you are cutting a circle could you not put a false hardboard or mdf top on the table and then use a pivot point at the apropriate centre so you can then rotate the wood on it for a perfect circle ( Ive done this lots on the bandsaw for bigger circles)

also you could use a plug cutting kit in a pillar drill to cut out the circles then just use the scroll saw to put teeth on them.

 

[gasmansteve]

could you not put a false hardboard or mdf top on the table and then use a pivot point at the apropriate centre so you can then rotate the wood on it for a perfect circle ( Ive done this lots on the bandsaw for bigger circles)

I did think of something along those lines myself as I`ve done a few times with my bandsaw and also with my disc sander. Not sure if the scrollsaw blade is rigid enough to allow a jig as opposed to the bandsaw as I say I don`t think I had my blade taught enough have to experiment. I even thought of securing the ply blank on my lathe off centre and cutting out the spokes with the parting chisel :?:
Regards
Steve

 

[Gill]

You would be much better off cutting a true circle with either a router or a bandsaw rather than with a scroll saw. Scroll saw blades have an inherent bias to the right, so the blade would be constantly trying to track away from the perimeter of the circle. How far away it could travel would be dependent on the sturdiness of the blade itself and its tension, but a degree of travel is practically inevitable.

In fact, Diamond did manufacture a circle cutting jig, but I've never been able to use it successfully because of this blade bias.

If I was cutting gears, I think I would adopt BSMs approach of cutting discs on another machine and then nibbling out the teeth with the scroll saw.

 

[gasmansteve]

If I was cutting gears, I think I would adopt BSMs approach of cutting discs on another machine and then nibbling out the teeth with the scroll saw.

I`m ok cutting the actual blanks for the gears and the teeth seem ok I use my band saw and disc sander for that, the circles and curves I want to cut are the internal ones that form the spokes of the wheels and look a bit naff to say the least cutting em freehand and really spoil the look. A jig would seem ideal providing the saw blade could be made rigid enough so it doesnt wander,that doesnt seem to be a problem with the external cuts made with a bandsaw and jig. Have to get me thinking cap on :wink:
Steve

 

[StevieB]

Late to this one, but I would echo the sentiments that your blade is too slack (allowing it to wander) and and too blunt (hence the failing to cut without excess pressure from you).

For 6mm ply I would go with a #5 for something that was not 'delicate' but routinely use the very fine superior puzzle blades on 6mm birch ply without any problem.

Steve.

 

[JAYJAY]

i cut 6mm ply regularly and find a #5 blade more than adequate, will say this though... i do have olson blades but only use them on larger cuts when using 6mm ply,
when i'm trying to cut delicate/intricate pieces or parts of a design i find them very aggressive and that they have a tendency (or possibly i have a tendency when using them) on tight turns and radius's that they can surge forward off the cut line and i find them harder to keep under control in the smaller areas of the designs, when i started scrolling and bought my saw and a bundle of blades i thought if i couldn't get it right with these blades (top of the range) i'm gonna be buggered with owt else and i may have just wasted a lot of money on a rather pricey garage ornament =(
sorry if i'm not making a great deal of sense here i'm trying to think of a way to explain what i mean but struggling to find some good england!! basically i think the olsons are so good and so sharp that they can be very unforgiving with plywood and the likes of me (a relative newbie to scrolling).
i seem to remember you saying in an earlier thread when we spoke that you got the reverse skips from always hobbies, i get mine from here too, they have a brandless/nameless reverse skip tooth blade just above the olson blades on their web page and i've been using these with a lot of my work (as well as the olsons blades), they do dull a lot quicker than the olsons and i don't get half as much use out of them before they need replacing but they're priced accordingly and i can buy 4 times as many in comparison. i just find these easier to keep under my control and much more forgiving at my level of scrolling daft as it may sound :?
not sure if i've helped here with what i've said and not sure if its got u closer to an answer but hope its made some kind of sense mate, thought i'd share all the same!!

 

[gasmansteve]

Thanks all for the very helpful replies. Don`t know why but never gave it a thought that the make of a blade could affect what you are after but then again with any tools I suppose that always applies :? . Have to give that Dutchman guys web site a look as well.
Cheers
Stevel

 

[gasmansteve]

JayJay had a look at those blades when they grade them as 5,7,9 I assume thats the same as #5,#7,#9. Have you tried the Yellow label blades too?.
Steve

 

[JAYJAY]

yeah, your spot on mate with the numbers thats exactly right, i struggled at 1st with hobbies and the way they listed items, it sometimes seems a bit backwards or here there and everywhere with which one your getting at which quantity and they sometimes have the same items listed twice but in different quantities and prices,they have prices for blades by the dozen and for the 12 dozon and so on and on (or i'm just a *******) keep an eye on your checkout total
as for the yellow labels .....yeah i've used them plenty and still do! never been overwhelmed but never disappointed either, they do exactly what they say on the packet ....sort of thing. i'll often use them and with the price they're at (bargain) when i started didn't mind buying a few at different sizes to experiment with especially when you can buy them in such small quantities
i find i don't really use any of the heavy ones or very rarely anyway for what i make and some of the light ones are really wafer thin like the '0' and '1' grade blades i do keep some at hand for really intricate work, but wouldn't want to cut to large area's with the light as it would take for ever. for what i do i mainly use the grade 5's again
i think a lot of the time there are several factors that come with your blade selection, what type of material your cutting how thick it is and how intricate your design as well.....and last but not least i think personal preference is a big thing probably with experience level thrown in to boot.
i'm sure you'll get and already have got some really good advice from everyone to help you get going in the right direction set up is vital you've got to make sure you start doing things in the correct manner 1st or you've no chance whichever blade you choose, but the last part of my paragraph rings true in my experience just starting out with scrolling, personal preference and experience level can effect it as well, like i've said ....me personally ...i struggle with the olsons blades on plywood especially with finer details but i'm sure there are those out there who wouldn't use anything other.
so give some of the cheap en's a go bud at least you won't have lost t much if they dont work out for you
JAY

 

[chrispuzzle]

The aggressive, sharp cut you get with top of the range blades can be an issue if you are trying to do delicate work on thin wood and the coarser the gauge the more aggressive it gets.

Obviously the thinner the wood the quicker a blade can cut through it so when aggression is an issue, the *ideal* blade to use is the smallest size of blade that will cut the wood comfortably, since the smaller the blade and the finer the teeth, the more control you get and the smoother the finish.

That said, we don't all have a ready supply of every different size and type of blade. It takes quite a while to get used to differences in blades and discover the best combination for you, the wood, your machine, and the piece of work. I guess that's the same with any craft and what makes the skills so personal.

I have a selection of Niqua "Yellow Label" blades from Hobbies that I often turn to if I am cutting very soft thin ply such as "lite" aircraft ply or when I'm using my Meccano fretsaw because I really don't want a very aggressive blade on a machine that's hard to control at the best of times. Looking at the teeth through a magnifier you can see that they are not as even or cleanly stamped out, and that is why the blade is less aggressive and will blunt faster.

I also know quite a few scrollers won't use a new blade directly on the work but make some practise cuts with it first to get a feel for it. I do that with very delicate work too. I don't want to ruin the work because the blade characteristics changed and my fingers hadn't noticed.

 

[gasmansteve]

Thanks for the advice Chris. I`ve been sent a few templates from Stevebuk (thanks again Steve!) to get my scrolling up to some kind of acceptable level before attempting these spokes again..What got my goat more than anything was that I`d been told beforehand that the hard part was cutting the actual gear teeth accurately so they mesh ok and I think I did ok with those. All part of the learning curve (theres that ruddy word again ) I suppose.
Cheers
Steve

 

[chrispuzzle]

Thanks for the advice Chris. I`ve been sent a few templates from Stevebuk (thanks again Steve!) to get my scrolling up to some kind of acceptable level before attempting these spokes again..What got my goat more than anything was that I`d been told beforehand that the hard part was cutting the actual gear teeth accurately so they mesh ok and I think I did ok with those. All part of the learning curve (theres that ruddy word again ) I suppose.
Cheers
Steve

Where the clock is driven by a synchronous motor (that is, a motor that runs at a constant speed regardless of the work it is doing) then the gears need to mesh OK and turn freely, and you're fine.

Where the clock is a weight-driven or spring-driven pendulum clock with an escapement wheel, the escapement needs to be perfect and the gears need to be very regular and even or the whole thing tends to seize up and not go at all.

This is because to get a decent length of time before rewinding the clock, the weight or spring will usually be asked to perform only the tiniest amount of work necessary to turn the hands and provide an impulse to keep the pendulum going. Thus pendulum clocks are usually designed to operate at the extreme edge of what is possible, and allow very little margin of error in the setting-up.

 

[gasmansteve]

Well after trying Steves templates I`m much happier now and realise where I was going wrong. 1-Blade much too slack think I didn`t want to overtighten for fear of snapping it and 2- I was rushing the cutting and going much too fast and also found I was pushing to the side making the blade distort. I gather scrollsaw blades have a tendency to veer off to one side so possibly thats what was happening. Guess I`ll stick with the Olsens for the time being.
Regards
Steve