March 20

Building a precision “Scroll Saw” or Jigsaw…

Back in my day (think 70’s and 80’s) we used to call table “scroll saws” jigsaws.  We called hand held “Jigsaws” Sabre Saws.  Well, I guess some all powerful authority decided that the names must be “switched all around” and now “Scroll saws” are the table variety and Jigsaws are the hand variety, and, well…

Anyway…

Scroll saws are a very nice tool to have in any Mad Scientist laboratory because of all the various things you can do with them outside of creating “scroll-work”… for example if you create printed circuit boards that are not square, but follow some weird shape due to the enclosure, or if you are making lost foam metal molds, or a variety of intricate cuts…. you need a precision scroll saw. sure you could get yourself a CNC water jet or some plasma cutter device and pay thousands, or… a scroll saw does the job much cheaper.

Problem is that a precision scroll saw is expensive.  Let me explain.

There are essentially 5 types of scroll saws out there. The spring tension saw, the parallel arm saw, the C-arm saw, hybrid parallel saw, and the oscillating saw. All of these saws have their pros and cons, and their basic configurations are shown here. If you look carefully you will see that each has issues with the saw blade that effect the precision of the cut.

constant tension

spring tension scroll saw

 

 

 

 

 

 

 

 

 

 

 

The spring tension scroll saw is a common one from the 50’s and 60’s but is not seen that much today even though the basic configuration is quite simple.  While the blade stays in the same place during the entire period of motion, the problem is that the tension on the blade changes – being at it’s highest when in the down position, and lowest in the up position.  This means that when the workpiece is pressed against the blade, the tension is in a constant state of weak, then strong.  This means that the blade flexes, and the cut will not be as precise as it could be.  It also means that the blade weakens and breaks much earlier than it normally would if it were under a constant tension.  The overall precision of the cut is compromised.

c arm

C-Arm Scroll Saw…

 

 

 

 

 

 

 

 

 

The C-Arm scroll saw as shown in the above picture has the advantage of keeping the blade tension constant, however as can be seen from the motion that is made, the blade position changes with respect tot eh cutting table and work-piece.  While very thin pieces may not be effected as long as the table cutting position stays constant as in the picture, thicker pieces will have issues with precise accurate cuts.  This becomes even more problematic if angles cuts are being used.  This is because the blade cantors back with the C-Arm as it goes through it’s periodic motion.

paralel arm

Parallel Swing Arm Scroll Saw

 

 

 

 

 

 

 

 

 

The parallel swing arm scroll saw is an improvement on the C-Arm, and also represents the oldest of the powered scroll saws in existence. Originally foot-peddle powered, these older saws had very deep throats upwards was three feet, making the offset that occurs when the saw moves upward or downward from center very minimal.  But as you can see in the picture above, this offset becomes much more noticeable as the arms become shorter as in modern day scroll saws.  Still, this is the mechanics of most inexpensive (under 200 dollars) scroll saws you can buy today.  Again, precision is lost because of the offset.

2 parllel

hybrid parallel arm scroll saw

 

 

 

 

 

 

 

A variation on the parallel arm scroll saw is the hybrid shown here which uses “rockers” to move a cam like series of mechanisms that moves the bald up and down, but again, because the final rockers that attach to the blade are set on a pivot, the blade will have some front to back loss of precision as it rotates around the center of the rocker pivot. more expensive scroll saws employ this method of blade drive to greatly reduce vibration of the saw, however the precision is still an issue because of the aforementioned rocker rotation.

So in all these cases, we have the design of the saw effecting either the tension of the blade during it’s travel, or the actual position of the blade! What we want is for the blade to stay put and only move up and down – nothing else!

There really is only one way to reliably move a blade up and down under a constant tension, without any loss of precision and that is shown below : The oscillating band driven scroll saw.  These types of saws are the most expensive, but are also the most precise scroll saws that money can buy.

oscillos

The oscillating band scroll saw – most precise money can buy.

 

 

 

 

 

 

 

 

 

Here is the deal: I needed a scroll saw.  I wanted one that was precise.  I’m a cheapskate. I like a challenge.

I decided to build my own.

I decided to build a precision oscillating scroll saw using a hybrid design that combines the band of the standard oscillating saw as shown above, and the “main rocker” idea of the hybrid swing arm saw.  Below is a simplified drawing of the saw I am building followed by the actual build itself.

scroll_saw_simple_des

Simplified diagram of my oscillating band style scroll saw. blade guide and other minor items not shown.

 

 

 

 

 

 

 

 

 

 

 

 

My version of the saw uses the rocker from the hybrid parallel arm saw, but then connects to the blade via a steel cable under tension as opposed to a continuous belt or band.  Using brass sliding door pulleys and a tension spring (not shown).  My current build progress is shown below.

scroll_saw3

Collection of junk to start with.

 

 

 

 

 

 

 

 

 

 

 

 

The collection of stuff I had on hand – those aluminum tubes I found in a dumpster next to house construction – by the way: House construction dumpsters are a wealth of great free stuff – but get permission first!  Usually they don’t mind because they have to pay a fee for every pound, and anything you take saves them money!

scroll_saw2

cleaning up the tubes (they had cement and oxidized tape on them)

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw1

cleaned up and cut to length.

 

 

 

 

 

 

 

 

 

 

 

 

By the way, you may have noticed behind the staks of cut tubing that I am building a mini Tesla supply – those door-knob caps are from Russia, bought them about a year after Chernobyl – I wonder where they came from?

scroll_saw11

assembling the frame

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw12

It’s coming together.

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw9

The combination of the two sets of struts makes the cantilevered arms of the saw very stiff.

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw5

Northern Tool Pillow Blocks – about 9 bucks a piece.

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw7

Pillow blocks mounted and shaft inserted.

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw14

The section for the rocker arm to be mounted to the shaft. Got to get the welder out!

 

 

 

 

 

 

 

 

 

 

 

 

scroll_saw10

Here are the brass pulleys for the saw…

 

 

 

 

 

 

 

 

 

 

 

 

motor

Old dryer motor for power…

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UPDATE! 03/13/2015 – nope, I still haven’t finished this thing, and I really need to because I really need a good jigsaw! Just too much stuff to do!

February 10

Culvert Pipe Food Dryer…

So I got me some leftover plastic Culvert pipe.

FoodDryer4

Plastic Culvert pipe has many uses…other than being for culverts.

What to do with this I thought to myself? Then it came to me… Make a food dehydrator out of it! So this is what I came up with…

FoodDryer

Finished Food Dryer with old blower from a Christmas “Blow up Snowman”

So using a old blower fan I had from a worn out Christmas “Blow up Snowman” some plywood, some plastic window screen, and a couple of “Banned” 100 watt light-bulbs, I proceeded to build this little contraption.

FoodDryer1

Those are real 100 watt “Edison Bulbs” – Contraband these days in the USA…

Using two ceramic light bulb sockets and 2 100 watt light bulbs I first created the lower section that generates the heat for drying. Note that there are concentric ring of holes around the bottom of the pipe and where the plywood meet so that air is constantly moving, carrying heat upwards.

FoodDryer2

single sections of pipe-rings with window screen held in by zip ties.

The pipe is cut into “Rings” that are done ins a way so that can stack like plates on top of each other. Then using plastic window screen and plastic zip ties, you create the food holding trays. As these are all high heat plastic (they withstand up to 400 degrees) they are dishwasher safe!

FoodDryer3

Hot water heater thermostat turns off the bulbs if things get too hot inside.

The blower goes on the top to suction the air out of the dryer and keep a constant flow of air moving. The metal dissipation plate forces the air to move around the food completely so there are not spots where air is trapped. The hot water heater thermostat is there as a safety precaution to shut off the light bulbs if it gets too hot inside.

I have dried tomatoes, bananas, many spices, etc in this dryer and it works very well. I would probably make the stack-able rings a bit more stable if I were to do it again, but all in all this is a single day project that can really add to your food processing skills and give you a bountiful harvest of dried seasonings, “sun dried” tomatoes, and other dehydrated delicacies!

-DTM.

February 7

A Cold Smoker for Meat and Cheese…

I like a good smoked cheese… Problem is, when you buy it at the store, it is very expensive.  Then you find out (if you care to look) it’s not really smoked at all! (at least not most of them).  No, instead most so-called “smoked cheese” you get at the store has been “Flavored” with liquid smoke, and then it’s been brined in a “colorant” that makes the outside brownish to give it that “Fresh from the smoker” look.

Pish -Tosh to all that! I want real smoked cheese!

hotsmoker

This can smoke your ribs… but not your cheese!

What to do?  Well you cant smoke cheese in a traditional hot smoker, such as a bullet smoker:

Not unless you like a burned, melted mass of glop.  I don’t prefer that…

No, Cheese must be smoked in what is known as a “Cold Smoker”.  I decided I wanted to smoke cheese and a variety of other things so it was time to build one of my own. So I decided to build mine as a 2 by 2 by 4 foot box out of scrap plywood as seen here.

 

 

smoker1

The Back of my smoker sticking out of my workshop on a cold day.

Here are several more pictures of the smoker…

smoker8

Front of Smoker

 

 

 

 

smoker4

Inside shot of the smoker showing racks and the smoke distributor on the floor.

 

 

 

 

smoker2

This shows the smoker with the racks and the distributor removed. Note the creosote collector – some spilled out when I was moving the smoker.

 

 

 

 

 

 

 

 

 

 

 

 

The smoker has a “smoke distributor” on the bottom – which is basically a false floor with large holes cut out to allow the smoke to permeate the entire box.

The smoke pipe runs down the entire length of the smoker so that the smoke cools, and so that creosote (which makes food bitter) is condensed and collected in a little tuna can at the bottom.  This has to be cleaned out after every smoking session.

The racks are 1.5 inch dowels that sit in cutouts on the side of the smoker.  The food to be smoked can be laid directly on the dowels, or (in the case of cheese and smaller items) placed on dollar store cookie cooling racks that then sit on the dowels quite nicely.

The door seals shut by using 2 lengths of cotton clothesline.  The clothesline seals against the door when it is shut for more or less an airtight seal.

smoker3

The Smoker loaded up with some chicken and a small turkey.

When loading up the smoker with meat, I always keep a drip pan underneath to try to keep as much of the raw meat drippings getting in the wood.  You cant stop it all. so you wipe down the inside with Clorox between smoking sessions (not needed when doing things like cheese or when smoking salt).

Now for the most important part of the smoker – the smoke generator!

The smoke generator is the box that sits atop my smokier, raised up in the air.

smoker9

The smoke generator.

 

 

 

 

 

 

 

 

I could have gone the rout of using a commercial smoke generator such as the “Smoke Daddy” Cold Smoke Generator but that would not be in keeping with my nature of “Build your own” – besides, the smoke daddy compels you to use their special “smoking wood sawdust chips”.  I wanted to use any kind of wood I can purchase from local sources, or cut from trees such as apple orchards, etc.

So, I built my own from an old Army Equipment box.  The way a smoke generator works is by using a negative pressure venturi inside an enclosed container which is where the smoking chips are burned without oxygen. The box is an hardened aluminum box with snap-down lid. The iron pipe goes through the center of the box, and where it passes through the box there is a hole. The arraignment looks like the schematic shown here.

SmokerSchematic.jog

The venturi (the blue tube that comes to a point in the diagram) pulls the smoke and keeps just enough air flowing into the box to keep the coals going once they are started from the two “touch-holes” on the outside of the box.  What happens is that the air moving through the venturi causes a vacuum in the larger tube which then pulls smoke and air from the seal box into the larger tube which then enters the box.  The larger tube is over 4 feet long so that the smoke cools down, and releases much of it’s creosote (a bitter chemical you don’t want on your food).

smoker6

Smoke Meat and Beer… Mmmmm!

The smoke then proceeds into the smoking box, where it emits from the base as cooled smoke.

Shown here, I am using Cherry Wood Chips purchased at my local “Harris Teeter” Grocery. The large beer next to the smoking chips is a delicious brown ale my brother Jamie made and bottled himself – nothing goes better with smoke and meat than a good, ice cold brew!

I shall update with more pictures of the smoke generator as I get time…

-DTM