Small Scroll Saw Build

[cfellows]

I've decided that a small scroll saw would be a nice addition to my shop.  However, my experience with the cheap, parallel arm scroll saws available from Home Depot and Lowes has been less than stellar.  I've decided to make my own rigid, C-Frame scroll saw to improve performance and take up less space.  My saw will have a throat of around 11".  Here's a few pictures...







The frame is made from 1/4" thick tool plate aluminum.  The overall dimensions were determined from material already on hand.  The blade clamps are made from 3/8" square steel rod, the end turned and threaded to 1/4" x 28 tpi for tension adjustment.  A 1/8" hole in the working end of the clamp will accept the blade end and an 8x32 SHCS on either side will clamp the blade in place.  The frame will rock on a 1/2" diameter drill rod axis which rides in 2, 1/2" bronze pillow block bearings.  The table will not have a tilting option.  Haven't decided how I'm going to power it, yet, but am thinking about using my sabre saw or perhaps a DC motor so I can vary the speed.

Chuck

[ShopShoe]

Chuck,

It's great to see you making another tool. I'll be following along.

From my experience with a cheap scroll saw I can say that I think that making the table without tilt is probably a good idea, as mine sometimes tilts when I don't want it to. It might be a useful feature if you could engineer a reliable adjusting and locking system, but based on the size I think I can visualize how you might use yours and tilt is probably not needed.

I would vote in favor of the variable speed idea: That is the one feature of my cheap saw that I really like. I use mine for a wide variety of materials and changing the speed makes it more adaptable to what I am doing.

Are you putting on a chip (or sawdust) blower?

--ShopShoe

[cfellows]

Thanks, Shopshoe, I have a couple of different DC motors, both 110v DC, but one smaller than the other.  Will try to get by with the smaller one, but if it doesn't have enough power I can always change to the larger one.  I have several rectified variacs around the shop to power it with.

Here's a picture of today's work.  Pretty much have the arm with blade clamps and tension adjusters all done. 



Just need to add the  1/2" drill rod axle that the arm will rotate on.  Then I can start on the base.

Chuck

[steamer]

That looks great Chuck!

Dave

[ironman123]

Keep it going Chuck.  Looking good.

[cfellows]

I have been working steadily on this project and have accomplished quite a bit.  I'll post some pictures and bring everyone up to date in the next few days.  I did want point out this little DC motor for folks that may have a use for something similar.  It's what I'm planning to use for my scroll saw.

http://www.ebay.com/itm/DC120V-2500rpm-High-power-DC-motors-Wind-Turbines-Generator-Ball-Bearings-/142023058434?hash=item21113be402:g:zJIAAOSwMNxXXYu7

It has a pretty good amount of torque, and it runs on 110v DC.  All you have to add is a cheap, full wave bridge rectifier and you can plug it in to 110v AC.  The no-load RPM is 2500 which is about right for many shop projects and it's surprisingly quiet when it runs.  Check prices, as this motor is available from a number of Chinese outlets.  May be available from a US supplier but will probably be more expensive.

Chuck

[cfellows]

Here are some pictures of my progress so far.  I pretty much have all the mechanical parts done and can now proceed to the base and enclosure which will be made from plywood.  Here is the angle iron bracket that will hold the drive unit.



Here is the crank bearing housing.  The bearings are 8mm ID.  The housing is made from 1.5" diameter cold rolled steel.

.

This is the assembled drive unit.  The spindle shaft is 8mm hardened steel.  The motor is rated at 55 watts and runs on 110v DC.



These are the brackets and bearings that carry the saw arm.  The bearings are 1/2" ID and the brackets are made from 1/4" x  2" aluminum angle.



And, here is a mock-up of what the assembled parts will look like.  Everything will be mounted inside a plywood box that is about 16" x 10" x 4.5" high.



The only mechanical piece left is the connecting rod and the crank pin.  Then I can start the enclosure and wiring.

Chuck

[crueby]

Wow - looking very good, nice and solid! I have a store-bought one, and can echo the votes to include a variable speed control for the motor, it comes in very handy to adapt to different materials as well as getting away from the resonant frequencies that it seems to hit now and then.

 

[cfellows]

Started working on the cabinet today.  Decided I needed to partially assemble things before I made the connecting rod.  Sometimes I don't trust my drawings as much as I do the actual work in progress... 





Never let it be said that I under-build things...



The arm moves up and down freely, but the only side to side movement is flex in the aluminum arm.  So far pretty much everything has been built with materials on hand.  The only thing I've bought are 12 carriage bolts.

Chuck

[Zephyrin]

Hi,
nice job you're doing with this scroll saw. And when you are at it, give to the lower blade clamp a good access for changing blades, it is difficult (and painful too!) on mine to see under the table ! 

It is a very useful tool, but i found that the limited stroke wears the saw blade on a too small part of its length, so I simply put a wood plate to increase the height of the working table and to prolong the life of the blade.

[cfellows]

Thanks, Zephrin.  I have given quite a bit of thought about access to the bottom blade clamp.  I've suffered from ill conceived designs in the past.  The front of the cabinet will be left completely open and the sides are angled in at the bottom so I can see the bottom blade clamp better.  I'm also going to cut a largish hole in the right side directly in line with blade clamp so I'll have a straight shot with a T-handled hex wrench.

Chuck

[cfellows]

So I've discovered I have  a problem with the geometry of the saw frame movement.  I put the center of rotation coincident with the table top thinking that.... well, not really thinking it through at all.



The stroke of the saw will be 3/4" and doing some CAD simulation, I see that this geometry will move the blade into the work on the up stroke and away from the work on the cutting stroke.  That can't be good.



So, I need to move the axis of rotation down 3/4".  This will move the blade away from the work on the up stroke and into the work on the down stroke.  By moving the axis down just the length of the stroke, the amount of horizontal movement will be kept to a minimum. 



Placing the axis even further down would increase horizontal distance of the blade movement and would most likely increase the aggressiveness of the cut, but would decrease the amount of control.  So, I'll stick with moving it just the length of the stroke.

Chuck

[crueby]

Interesting how the geometry works out. It made me go up and look at how my Ryobi saw works, and it turns out that has two seperately hinged arms, with a connecting link at the back. I always thought it was one big arm like you are making. I found this diagram:

It shows the pivots about a third of the way from the back of the arms, and the link up the back. They also have a counterweight on the eccentric that moves it up and down, are you planning something along those lines to reduce the vibration?
Interesting stuff!

[Noitoen]

I bought a scroll saw many years ago powered by a simple half wave rectified coil. The blade only moved by a couple of milimeters at the rate of 50 cycles per second. This combination made it "finger cutting proof". The main user was my 7 year old daughter tha had a lot of fun with thin plywood from fruit boxes.
The main draw back was the wear of the saw due to the small movement. I used some thin boards on the cutting table to change the cutting position on the blade.

[cfellows]

I still have some tuning and assembly to do, but I got it to a point where I could test it this evening.



I discovered a couple of problems right away.  Vibration is definitely a problem.  Some added weight and a counter weight on the crankshaft will help.  The other problem is the motor.  At 2500 RPM it's too fast and doesn't have enough torque when I dial the voltage down with the variac.  The maximum safe speed is about 50% of the rated voltage.   A constant speed electronic control would be great, but also complicates the project more than I want.  So, for the moment, I'm going to change the gearing.  I currently have a 12 tooth pulley on the motor and a 20 tooth pulley on the crankshaft.  I'm going to change to a 30 tooth pulley on the crank.  That'll let me run the motor at a higher voltage and provide more torque at the same time.  If  that doesn't work satisfactorily, then I will consider a constant speed motor controller.  Might be an interesting project in and of itself.   

Chuck