Metal Templates

[Gill]

Enough with the apologies guys ! I appreciate the sentiments but I can't help thinking that if we were all gathered together in a pub with a drink or two, the conversation would never have got quite so intense. Sometimes the written word lets us down and this appears to be one of those occasions.

Okay... these notions may be completely impractical but here goes...

For generations, woodworkers have valued dovetail joints as being decorative and effective. Unfortunately, they're not easy to cut by hand so a variety of jigs have been produced to help cut them, mostly in conjunction with routers. These jigs are often complicated to set up and expensive.

The traditional way of cutting dovetails (as I understand it) is to use a fretsaw to remove the bulk of the waste and a chisel to produce the final fit. Veritas has produced a set of anodised aluminium dovetail markers to help mark out dovetails for cutting by hand:

Veritas Dovetail Markers

I can't help thinking that running a powered fretsaw along the edge of these markers would make the cutting of through dovetails easier, faster and very accurate. It would enable scrollers to produce presentable boxes without going to the trouble of either mastering rather difficult joinery techniques or buying an expensive jig.

If a metal that is harder than the blade is used for the dovetail template, it should be possible to run the blade along it without cutting into it. I realise blades have an inherent bias (usually to the right) but this shouldn't be a problem because if the blade veers away from the template it will be cutting into waste wood; if it veers into the template, it will simply stop cutting the wood at all and the tone of the blade will change, indicating that the scroller needs to veer away a little.

Gill (who's wearing a tin hat )

[GrayBeard Phil]

Ok, Here is my long winded, OT reply.

Gill:
Please don't take this as a pile on, this is just some rambling thoughts of mine.

In traditional usage, a template is used for making repetitive cuts. For example, one wants to make 100 copies of a pattern. Sometimes someone makes a fixture to hold a work piece, or a jig to assist in tool alignment, or a guide to aid making an accurate cut. Like your last post about the dovetail jig. For now, lets call the entire class as manufacturing aids.

There is a lot of thinking that goes into design, fabricating, testing, trial, re-fabricating, testing, and finial useage of manufacturing aids. A whole lot of effort. If one is making 100 copies of a puzzle, then yes, the effort can be justified.

For the most part, scroll sawyers free hand the wood past the cutting teeth of the blade. Most of us have a pattern fixed to the stock to guide us. My guess, and this is just my guess, what attracts us to the hobby is the non-robotic nature making of an object, albeit as accurate as we are able. But the practiced skill of free handing the wood along the cut line is exactly what draws me to this hobby.

Now, I will try to explain it this way. Think of the idea of a plastic tube surrounding a scroll saw blade. Just try to visualize it, ignore for a moment the problems of friction, heat, sawdust and chip removal, air blowing, sighting and so forth. As you think about your last project and how you rotated your work around the blade, you will come to realize the sharpest corner you will be able to make with a 'guide tube' is the diameter of the tube. Even I cannot write a post long enough to explain my reasoning here, but I can prove it. You will not be able to cut a corner sharper than the tube, if the tube is ridding against a template.

So, in the next exercise, let us imagine a very small diameter (say 10mm) post, fixed 1.00 cm to the right of the blade, but in the same plane (front to back) as the cutting teeth of the blade. Long story short, if you are making inside cuts such that the wood removed looks like a Oak Leaf, it won't look like an Oak leaf. In my thinking through this problem, I keep running to the displaced mapping of the piviot point from one place on the plane to another. As the work piece is rotated,..... Well it is a long 2 hour lecture as to the errors and problems this causes and why modern factories hate guide pins rubbing against edges of templates. This is why they came up with ball bearing guides.

As I look at all the problem, I keep coming back to the point that the scroll saws machines on the market today are designed and made for the free hand feeding of stock past a fixed blade that is oscillating up and down.

What if you only want to make 20 or 30 copies of something?

The first thing that must be discarded is the table being fixed to the frame of the saw. What is needed is a very heavy frame that can move in an X and Y fashion, and then rotates completely around. Directly attached to the frame, or by use of a sacrificial support, the project wood is affixed. Now think of a pantograph device that is fixed to the frame and by using a guide pin can control the X and Y direction of the Frame; while the rotation is done by the operator as needed to make the sharp corners.

Since I cannot explain this well enough to myself to draw this out, none of you reading this can possibly have any clue of what I just said. But let us move on and just imagine the following, you still have to make the re-usable template, you still have to have someone run the machine, rotate the holding fixture, and move the pointing device along the template.

That is still a lot of effort.

Just take my word, that as you continue to think through this process you begin to understand the reason so many have moved up to the infra-red laser cutter, with head controled by CNC computer software. ( I do not recommend the high pressure water cutters for use with solid wood.) Aside: a 'home brew' system can be built for about 3 to 4 times the cost of a Hawk, or Hegner.) And you can program the 'kerf' to be as wide as you want without changing blades.

However, once you cross over away from the current design of scroll saws, you leave the hobby / craft world of scroll sawing. You have entered the world of manufacturing. This is not where I want to be.

Phil

PS: Gill:
Mark Duginske (author of Bandsaw Handbook) and others have published articles in Fine Wood Working for making jigs for a bandsaw and fixtures for doing as you have posted. If at all possible find a copy of Woodsmith (http://www.woodsmith.com/) issue #66 for a jig that can be modified for your Diamond saw. This article covers problems with the importance of highly accurate table tilt to match Tails and Pins. Very Nasty problem the mating angles matching between tails and pins when machine cut.

[CanadianScroller]

The dovetail jig?

Hi Gill, the dovetail template you posted is a great idea.
I once saw an auxillary table that went onto a bandsaw for cutting dovetails.
The table was raised in the middle and rocked back and forth like a see saw
Set the table on one side and cut one half of the dovetail, tilt it the opposite way and cut the other.
If you are interested I will see if I can scrounge it up for you and post it.

[Gill]

Phil

That's a very detailed response and you've clearly given the matter a lot of thought; thank you. Nevertheless, I still don't see how your reservations would impact on a simple device for cutting straight lines accurately such as the dovetail template I've described.

Carl

I think I can imagine the sort of jig you're describing - a V-shaped bed to carry the wood? I'm not sure we'd need this sort of gadget because it's very simple for scrollers to adjust the saw table to an angle of 7 or 8 degrees and cut accurately.

To my mind, the biggest problem with using the dovetail templates would be securing them to the wood whilst cutting. The only way I can imagine doing this would be to have 2 very short, fine pins that would bite into the endgrain.

As a non-engineer, I'm still none the wiser as to what material the templates should be made from.

Gill

[Thomp]

Sorry folks,

ive pondered this question for a long time before, and felt it necessary to add my 2 cents worth,

gill if this discussion is about a template is for making a perfect dovetail with a scrollsaw, good luck,

i think box joint is possible but with much more effort than an alternate table on a router table

i have made many attempts to use jigsaw bandsaw router and dovetail handsaw and chizzles to achieve a good dovetail joint, and have pondered the making of a dovetail or box joint on the scrollsaw,

but i always return to the hand tools. and still fail on a regular basis.


the metal to make the jig out of that would be harder than the blade , you might find a metal urgest(sp) as this is their speciality.. i would think high carbon nickle with molyvelienum or other substance, like used in kitchen knife blades, or hardened chromed metal like ball bearings are made of.
it would inhibit template wear,
or maybe completely made of ceramic, but ceramic would dull the blade instantly i would think, and shatter if it hit the floor.

where the high carbon nickle with other wear resistant propertys might do the same you could make the template extra thick to spread the wear over many teeth and do less dulling on the blade in single contact point as a thin template would do..

http://www.use-enco.com/CGI/INSRHM a machiene shop supplier. it sells different types of metal for machienists & metal urgests and you might get an idea there or find techinical data sheets on specific wear propertys they have produced..

[arbarnhart]

In the other recent thread about following a metal guide, I mentioned having some success by using a stone on the blade to remove any set in the teeth, in essence producing a flush cut blade. It makes the hardness of the guide less of an issue.

Using guides in this fashion, corners have to be where cuts meet, not where a blade turns. That can work out with extra cuts as long as the interior is waste, like it is in a dovetail.

NOTE - I don't think the scroll saw is the best choice, but my experience with following metal guides was reasonably successful. YMMV...

[sawdustus]

sawdustus of hiawatha

Gill,

I know this does not answer your template question and I hope I am not repeating information that is a trade or professional secret but my wife and I were at the recent Fox Chapel open house and had the pleasure of watching and listening to Gary MacKay. He was mostly demonstrating how to cut the fantastic designer corner joints he has created for his beautiful scroll saw boxes (see Issue 24). As an aside, he mentioned that he had developed a technique for cutting dovetails on the scrollsaw that was very easy (for him). He basically cut the compound angles by twisting the ends of the blades 90 degrees, remounting them in the saw, and then tilting the table. This had the effect of the blade cutting directly to the right as he faced the saw thus cutting the compound angle of the dovetail. You had to be there to believe how accurate and fast he was. I am sure that practice has made him nearly perfect and that he threw out dozens of trial pieces.

[Gill]

Interesting. I can rotate the blade holders in my saw through 90 degrees which would make the process even easier for me. I'll have to try the technique myself one day.

Thanks for that, George .

Gill

[CanadianScroller]

Gill I am still thinking about the saw guide I talked to you about before. I will have to make one over Christmas and let you know the results.

I think it would work quite well for miters and fingerjoints. It wouldn't work on blind dovetails though.

I will keep you posted.

[BirdOasis]

In a book I checked out from the library I saw that they like to use thick plexiglass to guide the blade. This makes it much faster to cut the template.

Now if you cut only on the left side you'll avoid that dreadded bur. Wouldn't you?

I would imagine that metal would get cought in the teeth, but it's an interesting thought.

[CanadianScroller]

my guide idea

Well I was going to wait till I actually made this but I don't know when I will get time so I am posting the idea on here and if someone makes one that's cool.

I think this will work. you would need to use spiral blades. The pressure on the blade will of course cause the blade to bend somewhat but I think with care this should work.
Another option would be to contact a blade manufacturer and see if they could make the bottom part of a spiral blade toothless up to the point of the bushing.

Gill could use a dovetail template, you could cut perfect miters and do fingerjoints with an appropriate template.
You could also mass produce pieces for tole painting.

If anyone makes a fortune on this remember me in your will

[Albert]

That would work, Carl. The pattern would be on the bottom and its thickness would be equal to or thicker than the bushing's height. This is just the same as a router with a pattern bit having a bushing or bearing on the bits end. It's even easy to set up: just epoxy a tiny piece of brass pipe, or round bar with a hole drilled, or a brass nut with the outside ground round.

[Neal Moore]

The concept looks great on paper Carl but if there was very much waste material extending beyond the template it would likely create excessive "chatter" in as much as the work piece isn't flat to the table.....then again...maybe not???