Author Topic: Small Scroll Saw Build (Read 10887 times)

cfellows · « **on:** June 15, 2017, 06:02:56 AM »

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 · « **Reply #1 on:** June 15, 2017, 01:43:57 PM »

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 · « **Reply #2 on:** June 16, 2017, 05:38:47 AM »

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 · « **Reply #3 on:** June 16, 2017, 11:40:25 AM »

That looks great Chuck!

Dave

ironman123 · « **Reply #4 on:** June 17, 2017, 01:44:57 AM »

Keep it going Chuck. Looking good.

cfellows · « **Reply #5 on:** June 19, 2017, 07:02:14 AM »

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 · « **Reply #6 on:** June 19, 2017, 09:34:49 PM »

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 · « **Reply #7 on:** June 19, 2017, 09:38:42 PM »

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 · « **Reply #8 on:** June 21, 2017, 03:32:14 AM »

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 · « **Reply #9 on:** June 21, 2017, 07:52:17 AM »

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 · « **Reply #10 on:** June 21, 2017, 03:51:40 PM »

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 · « **Reply #11 on:** June 21, 2017, 05:12:51 PM »

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 · « **Reply #12 on:** June 21, 2017, 05:29:26 PM »

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 · « **Reply #13 on:** June 21, 2017, 05:35:42 PM »

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 · « **Reply #14 on:** June 22, 2017, 05:11:06 AM »

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

MJM460 · « **Reply #15 on:** June 22, 2017, 08:07:20 AM »

Hi Chuck,

Been quietly following along on your great project. Great to see you in the shop again.

My commercial unit, actually it's my daughters, but stored in my shed, vibrates a lot too. The commercial approach is to put on thick vibration absorbing feet, not very sophisticated.

It is an interesting problem to balance as you have the not only the unbalance of the frame moving up and down but it has a small amount of rotation as well.

I suspect that if you attach a weight on the back of the frame (might need an opening in your back board so it is not ugly above the cutting table) to balance the frame around the pivot (with blade and the little con rod in place), you could get a pretty good result. If you really want smooth, the weight has to be on an arm geared to the frame so the weight moves up and anticlockwise as the frame moves up all the while in static balance. But even Marvin might think that was over the top. Keep is simple will probably still give you the best balanced saw in the known universe.

MJM460

MJM460 · « **Reply #16 on:** June 22, 2017, 09:56:51 AM »

Sorry Chuck, just noticed that I had missed a few posts. If you are moving the pivot anyway, might as well shift it towards the blade to the balance point as well. Always better not to add weight to a forced vibration.

Chris's four bar linkage Ryobi is an interesting approach to both the blade advance and balance problems though it will still move a little towards the work on the up stroke. We need to work out an orbital mechanism like the jigsaws. That really helps clear the chips. I must go out and have a closer look at mine. Too cold now but I will report back.

MJM460

cfellows · « **Reply #17 on:** June 22, 2017, 03:12:26 PM »

Quote from: MJM460 on June 22, 2017, 09:56:51 AM

Sorry Chuck, just noticed that I had missed a few posts. If you are moving the pivot anyway, might as well shift it towards the blade to the balance point as well. Always better not to add weight to a forced vibration.

Chris's four bar linkage Ryobi is an interesting approach to both the blade advance and balance problems though it will still move a little towards the work on the up stroke. We need to work out an orbital mechanism like the jigsaws. That really helps clear the chips. I must go out and have a closer look at mine. Too cold now but I will report back.

MJM460

Thanks for your comments and suggestions. The parallel arm linkage like the Ryobi is, by far and away, the most common mechanism used in today's scroll saws. However, the C-Frame design, like mine, is purported to enjoy a longer blade life and the overall design can be kept smaller. And, since there is only one pivot point instead of 6, it's mechanically easier to control unwanted blade motions caused by play in the pivots. The trade-off, of course, is vibration.

I have several options for mitigating the vibration and will continue to report on how I'm doing.

Chuck

cfellows · « **Reply #18 on:** June 23, 2017, 05:17:25 AM »

Rummaging through my stash, I found a 10 tooth timing pulley that will fit on the motor. I decided to make a 30 tooth timing pulley for the crankshaft. I'm making it out of brass to add weight and provide some flywheel effect. I have a 3/32" thick slitting saw that I modified to cut XL timing pulley grooves.

The outer diameter is 1.89", the hub is 1.25". Overall width is about 7/8". I've designed I new crank disk that will have counter balancing. If that isn't enough I can also cut away part of the web on pulley to add more counter weight.

Tomorrow, I will use my CNC mill and 4th axis to cut the grooves.

Chuck

cfellows · « **Reply #19 on:** June 24, 2017, 02:34:07 AM »

So here's a multi-part video. The first couple of segments show the process of cutting a 30 tooth, XL timing pulley. The last segment shows a test of the scroll saw with new pulleys in place.

<a href="https://www.youtube.com/watch?v=TPgbOhfXK0g" target="_blank">http://www.youtube.com/watch?v=TPgbOhfXK0g</a>

Chuck

cfellows · « **Reply #20 on:** June 25, 2017, 03:32:22 AM »

Here's some pictures...

This is the 12" x 5" x 1/2" steel plate attached to the bottom of the saw:

And here is the drive unit with the new pulleys and the new brass, counter-weighted crankshaft:

And here it is all buttoned up, including the switch:

All the balancing measures and slowing down the drive has the saw behaving pretty well, not much vibration. I had no idea how big of a counter-weight to put on the crank, but it did help. I may have to put a bigger motor on it, which won't be a trivial matter. It's kind of bogs down on 1/2" or thicker plywood. I really made it to cut thin materials like plastic or plywood no more than 1/4" thick, usually even thinner. I'll use it for a while and see how it works out.

Chuck

Kim · « **Reply #21 on:** June 25, 2017, 05:54:20 AM »

That is a really nice little scroll saw you made there, Chuck!
Now what are you going to make with it?
Kim

MJM460 · « **Reply #22 on:** June 25, 2017, 08:36:29 AM »

Hi Chuck,

That is a great result. Good to see that your solutions to the problems worked out well. I like the creative use of the brown stuff, it probably even adds a bit of damping.

Complete balance is tricky to achieve because the frame motion has a component of rotation, and that needs a counter rotating couple for complete balance, and almost certainly not worth the complexity. Anyway it is a forced vibration scenario and your heavy plate underneath is quite a valid way to reduce the response.

You could probably test if your static counterbalance is good by slipping off the belt and spinning the crank. If it always stops in the same spot, the low side is still heavy. If it tends to stop at many or even just a few places your balance is probably as good as you will get.

Earlier I said I would check my daughters Delta machine. It has the extra pivots like the Ryobi. I think the elegant simplicity of your design beats the complexity, particularly for such a handy small machine. If you need to cut 1/2" stuff, perhaps the next project could be a band saw.

MJM460

cfellows · « **Reply #23 on:** June 25, 2017, 04:03:14 PM »

Good idea on removing the belt and spinning the assembly to see where it stops. Hadn't thought of that, but will give it a try today.

Thx... Chuck

cfellows · « **Reply #24 on:** June 26, 2017, 04:13:51 PM »

Round 3... I checked the balance as MJM suggested and found that the counterweight I built into the crank wasn't anywhere near enough. Because everything is mounted in ball bearings, it all moves very freely so I didn't even have to spin it. I just turned the weight to the top and it rotates right back to the bottom.

So I'm going for round 3 on the Crank. I'll get the new crank done today and include some more pictures. I'm also not happy with the power of the little motor I started out with, so I'm replacing it with a larger, 90v DC motor. The first motor was 1.75" tall and was just barely cleared by the bottom of the arm. The new motor is 2.5" diameter and won't fit under the arm, so I'm mounting it out front where there is no clearance problem. It's still tucked back under the case far enough that it's not too unsightly.

Chuck

DICKEYBIRD · « **Reply #25 on:** June 26, 2017, 07:49:55 PM »

Quote from: cfellows on June 26, 2017, 04:13:51 PM

I'm also not happy with the power of the little motor I started out with, so I'm replacing it with a larger, 90v DC motor.

What kind of motor did you come up with Chuck? I'm always looking for 90vdc motors that are smaller than treadmill motors. Did you find an inexpensive Chinese one?

cfellows · « **Reply #26 on:** June 26, 2017, 11:33:46 PM »

Quote from: DICKEYBIRD on June 26, 2017, 07:49:55 PM

Quote from: cfellows on June 26, 2017, 04:13:51 PM
I'm also not happy with the power of the little motor I started out with, so I'm replacing it with a larger, 90v DC motor.
What kind of motor did you come up with Chuck? I'm always looking for 90vdc motors that are smaller than treadmill motors. Did you find an inexpensive Chinese one?

Unfortunately, I acquired the motor many years ago, I think from Lincoln Surplus Center.

http://www.surpluscenter.com/

I looked on their site and couldn't find it. I had the voltage wrong, it's rated at 100 volts and no-load speed is 3000 RPM. Dimensions are 2.5" x 5" long, 3/8" shaft. Guess that doesn't help you if you can't find one. The part number is E51964 BPM1012. It's been sitting in a drawer for 12 or more years, so I'm guessing your chance of finding one are pretty slim.

cfellows · « **Reply #27 on:** June 26, 2017, 11:38:46 PM »

Got the counter-weighted crank done today. Turned out nice, but it's still not heavy enough.

Not doing any more with the crank. Might hollow out one side of the brass drive pulley to remove more weight from the light side. I'm going to put it together and see how it behaves.

Chuck

DICKEYBIRD · « **Reply #28 on:** June 27, 2017, 12:01:35 AM »

Thanks for checking on it Chuck. I'll bump into something one of these days. I like the 90v range because I have a few extra KBIC-120 speed controls lying around & they work great.

I picked up a 24vdc scooter motor cheap on ebay & run it @ 38v on my homemade toolpost grinder. I took it apart & added some cooling holes plus broke it in carefully. Seems to do pretty well but I'd like more power eventually.

Could you drill a couple holes & fit some scrap carbide chunks in your counterweight? I think carbide is at least twice as heavy as brass. Dunno if it's worth the trouble but it might be an interesting experiment.

cfellows · « **Reply #29 on:** June 27, 2017, 01:30:13 AM »

So, I got everything put back together. A couple of observations. Supposedly, the smaller motor had a maximum speed of 2500 RPM and the larger motor I just installed was supposed to run at 3000 RPM. Well, the new motor runs a lot faster than the smaller one, maybe close to twice as fast. Fifty percent voltage on the variac is about as fast as I want to run this thing. Vibration is less with the new crank, but at anything over half throttle, it starts vibrating quite a bit. The good news, this larger motor has way more than enough torque and I can run the saw at a very slow speed without it lugging down. With its 3/4" stroke, it cuts 3/4 inch plywood aggressively, even at slower speeds, and gives me a really smooth, controllable cut. I'm actually very pleased with the results. However, I think the addition of a hold-down foot is going to be a requirement. More on that after a little design work.

Chuck

crueby · « **Reply #30 on:** June 27, 2017, 01:50:01 AM »

On mine, I find that I rarely run it at its full speed, usually just fast enough to cut cleanly but allowing me to follow the curves. And the hold down foot is a must for small and thin parts. Some include a guide for the back of the blade to reduce flexing.

MJM460 · « **Reply #31 on:** June 27, 2017, 01:52:04 AM »

Hi Chuck, glad disconnecting the belt was a help. I suspect there are diminishing returns on what you can achieve with the crank counterweight, as you are effectively adding a rotating force (the full 360 deg) which cannot completely balance either the primarily up and down motion of the frame, or the rotary oscillation caused by the pivot point.

Probably is worth clamping a weight to the back of the frame, to see if getting static balance is enough. The multi pivot design is obviously more nearly statically balanced so I expect you will achieve as much as they do, even though that is not perfect, as it does not balance the oscillating rotary motion. If this works well enough, then figure out how to put the weight below the table, out of sight. Or move the pivot to achieve balance without adding weight. If still not enough, we will need to discuss how to completely balance that rotary oscillation.

MJM460

Ian S C · « **Reply #32 on:** June 27, 2017, 03:31:43 AM »

to add more weight to the crank, you could drill two or three large holes in the side of the counterweight, and fill them with lead, might be easier than carbide.
Iwas wondering if a counter rotating balance shaft might do the job?
I'v been eying up an old Black & Decker drill attachment jigsaw with the idea of making a small,6" to 8" throat saw to take fretsaw / piercingsaw blades, but you saw looks a better design.
Ian S C

cfellows · « **Reply #33 on:** June 28, 2017, 11:02:05 PM »

I'm calling it good-nuff. I can run the saw at 50% speed and it cuts plenty fast with very little vibration. No bogging down. On the front of the enclosed video are a few still pictures of the finished saw along with a video of me cutting some 3/4" plywood.

<a href="https://www.youtube.com/watch?v=q-cQm_xTMVg" target="_blank">http://www.youtube.com/watch?v=q-cQm_xTMVg</a>

Now, let's see, what's next on the project list...

Chuck

10KPete · « **Reply #34 on:** June 28, 2017, 11:22:00 PM »

Chuck, that's about as smooth and fast as anyone could care about! That's a goin' rig.

Congratulations!

Pete

crueby · « **Reply #35 on:** June 29, 2017, 12:27:01 AM »

That looks great - cuts like that in 3/4" ply, couldn't ask for more from it. Nice!

Kim · « **Reply #36 on:** June 29, 2017, 03:19:20 AM »

That is pretty slick Chuck!
I've enjoyed using my scroll saw, but it will be that much more satisfying using one you made yourself!

Kim

MJM460 · « **Reply #37 on:** June 29, 2017, 11:03:26 AM »

Great result Chuck, and very satisfying to use such a handy machine you have made yourself.

Next project? Obviously something needing a good scroll saw! Hmmm......

Congratulations on a successful project.

MJM460

ShopShoe · « **Reply #38 on:** June 29, 2017, 02:41:52 PM »

That is nice and takes on that three-quarters plywood better than my cheap "bought" one.

I really enjoy your tool and machine builds.

Thanks for posting.

ShopShoe

crueby · « **Reply #39 on:** June 29, 2017, 07:21:01 PM »

What brand blades are you using Chuck? I found on the jig saw that the blades made a huge difference.

Ian S C · « **Reply #40 on:** June 30, 2017, 02:52:39 AM »

Chuck, does it still have enough power when it is slowed down enough to cut metal such as brass or aluminium, maybe 1/8" thick?
Ian S C

cfellows · « **Reply #41 on:** July 01, 2017, 04:32:21 AM »

Quote from: crueby on June 29, 2017, 07:21:01 PM

What brand blades are you using Chuck? I found on the jig saw that the blades made a huge difference.

I have some Olsen blades which cut pretty aggressively but don't leave a very smooth finish. The one I'm using in the video is a no-name blade from Ebay. I bought a large assortment of different blades pretty cheap, so I'm guessing the quality isn't great.

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Author Topic: Small Scroll Saw Build (Read 10887 times)