Meccano Mk II Scrollsaw

[chrispuzzle]

I posted details of my Meccano scrollsaw on the "welcome" forum when I introduced myself. The idea is to fiddle around building my own saw while I save my pennies waiting to buy a "proper" saw. Carl suggested some improvements and I have added some of my own. Here is the Meccano Scrollsaw Mk II.

I am using a more aggressive motor and getting up to 400spm, at a rough guess, before it starts hammering and trying to fly off the bench. I will have to try and calibrate the speed. The clamps are now pivoted (thanks Carl) and have a quick release mechanism (a collar with grub screw) although you still have to clamp the blade into the pivoting strips. But if you pre-clamp the blades you can easily change the assembly. The turnbuckle to adjust blade tension is also much more robust with less play in its bearings. I also added a big spoked brass wheel as a flywheel on the crankshaft.

My first pass found it tough to cut wood. The Meccano Scrollsaw MkII was cutting 3mm birch plywood this morning from a 4cm square piece of scrap wood, so it's definitely improving. I have added a picture of the puzzle so you can see how small the cuts are (using a Niqua 2# blade) with the saw. The pieces average about 1/3 of a square inch, or about half "normal" puzzle area.

Chris

[Gill]

Hi Chris

Have you thought of contacting Doug Woodward or his son Paul? Doug manufactures the Diamond fretsaw but he's elderly and doesn't have anyone to succeed him. I'm sure he'd be only too happy to take you through the construction process and offer advice.

Gill

[chrispuzzle]

Hi Gill -

I haven't thought of doing that yet. My limitations come from a system that uses mild steel, 8-gauge piano wire axles and 5/32" BSW screw threads in much looser holes at 1/2" spacing. Meccano was designed to be a sloppy fit, as is sensible for a children's toy. I am sure that at the heart of Doug's approach will be anything but sloppiness - the best machining, the best materials, everything designed with one purpose in mind.

Now I can see a lot of things wrong with the Mk2 saw already! It needs weight to stop it wandering around the bench top. There is still too much play in the arm at the bearings and the table wants to be more robust now that the motor is putting out more torque and I am cutting wood, not foam core.

I can see Doug Woodward snorting in amused disgust at the current version...on the other hand, it would be fun, wouldn't it...

Chris

[workin for wood]

Send me your address, I will send you a straight jacket as an award for most interesting yet insane scroll saw. If your honestly building this because you can't afford to buy a saw, I'm sure you could get a saw for free by just asking. If your in Michigan, I'll give you my old sears saw. It's big and heavy like a boat anchor. 18" throat, piston drive. It's not a pro saw, but I've mastered it to make some great scrollings. I bet there's others like me that would have an extra old saw laying around you could have.
I do wonder why they don't make piston drive saws anymore...this one is 99 percent vibration free. The arms don't get in the way so much either, much more clearance. It has no tensioner, but I've discovered if you clip blades slightly shorter, they become more taught.

[CanadianScroller]

Chris, your modifications are awesome.
I am really impressed that you were able to cut wood.
This is a really fun project to watch develop.
I have some other ideas you might like to explore. Just drop me an email and I will be glad to share them.

You are right about the increase of mass in the base to reduce the vibration.
As for the table, you may want to use a pice of thin ply bolted to the top with a small pilot hole for the blade.

I know the whole design is based on the parallel arm system, and that means you need 2 bearings, four if you count the blade pivots, Have you thought of a "C" arm construction like some of the Delta's that would reduce the number of pivots, and moving parts.

Here is a link to some more designs you may get some ideas from.
I do have an idea for a saw you could make with Meccano that would be virtually vibration free. It uses scotch yokes and drive shafts.

Anyway. I am getting away from what I first wanted to say...Champion job!

Carl

[Gill]

Originally Posted by chrispuzzle

I can see Doug Woodward snorting in amused disgust at the current version

Hi Chris

I know Doug and I can tell you that whilst he'd certainly be amused, he'd also have respect for a fellow engineer who's made an effort to design and produce a working saw. In the 'old' days, Diamonds were made by three engineers plus staff in a factory unit and they manufactured their own components. Doug is the only survivor and the factory is no more. He now produces saws in a wooden workshop at the end of his garden, largely using pre-fabricated components. Basically, he plays with Meccano too, but his set is more sophisticated than the one you're using .

I'm sure Doug would be only too happy to help you develop your saw into something more practical.

Gill

[chrispuzzle]

Jeff - Thanks for the straitjacket award! And thank you for the very kind offer - but I live in London in the UK, a bit of a long drive to Michigan. I'm also not that impoverished. What happened was that I asked for advice on buying a saw from the UK woodworking group, and immediately realised I probably wanted to spend about twice as much as I had budgeted. So I thought I would make the Meccano saw to have some fun while I wait to buy a $400 saw instead of a $200 saw. I'm looking at the new Axminster at the moment - http://www.axminster.co.uk/product-A...tsaw-32495.htm - which Gill says looks like a Hegner clone.

But I'm having so much fun with the home-made saw that I shall probably keep that project going for a while anyway. Meccano is a big hobby of mine and I can see the Meccano saw being very popular at exhibitions.

Chris

[chrispuzzle]

Carl - Thanks for the praise. And the links are amazing, I love the one made out of an upturned sewing machine, some twobyfour, and an iron drainpipe. This is the engineering that won the West...

I did think about a C frame and certainly it means fewer moving parts. It would have required putting the tensioner on the end of the arm, though, which adds considerably to the weight when you consider the leverage the end of the arm is exerting. It seemed to me having that stuff behind the main bearing helped - even if only slightly - to balance the arm. That makes me wonder, as I write, whether a counterweight would be helpful or counterproductive.

Gill - Well I am a little shy of approaching the legend! I will think about it and maybe do a few more 'improvements' first. But yes, I know a lot of old engineers who like fooling around with stuff. Maybe I will pluck up my courage and get in touch with them.

Chris

[CanadianScroller]

Another thought on the C arm.
What if the tension was built into the mechanism that has the pitman arm on it. That way the mass is closer to the center of the moving parts. That would reduce vibration.

We tend to apply an increase in tension after the blade is clamped.
If the tension is an intregal part of the frame, and we reduce the tension to facilitate the clamping action. the "normal" tension could then be restored as the saw is operating.
This would certainly reduce the mass of the moving parts and reduce vibration

I would love to try all this with Mecanno but I went to the store yesterday to look at a few sets. That hobby costs more than scrolling

I still want to explore the drive shafts and scotch yoke ideas.

[workin for wood]

I think you should use the older piston style. That's alot less vibration and less need for weight. It's a cam shaft underneath basically, and on the top arm is a piston with a spring under it. The bottom part pulls down and the spring up top pulls the blade back upwards. The motor can be directly attached to the cam shaft. Anyhow, I do think your saw looks cool. It's perfect for sitting on a shelf as a conversation piece. It would be great for taking to shows as well, for grins, giggles and conversation. I hope when you can get your new saw it works well for you.