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The Heavy Duty

Adjustable stroke length and depth for $150

I will often get asked, "What is the most basic build you can do and still have a functional machine?" 


Well, here it is... For me, this is as basic as it can get and still maintain full functionality. When I say that, the machine has to be portable with both adjustable speed and adjustable stroke. I also wanted this to be a machine someone with little experience and few tools could make in a couple of hours.


Additionally, I designed this machine with the following goals:
- Easily obtainable components
- Little to no machining
- A final budget under $150 but adjustable stroke length and motor speed


Using a low-RPM drill from Harbor Freight, I added the speed control and made a few parts from what I already had in the workshop. 

All in all, I figure the budget breaks down like this:
$45, drill from Harbor Freight
$25, speed control
$10, sheet of 16" x 3' wood, 1/2" thick
$10, 3' of 3/4" aluminum tube
$25, Delrin from eBay (I used this to build the guides and the Vac-U-Lock adapter)
$25, misc rod parts, bolts, etc.

Here is a video of the machine:

The Drill

I used a simple 1/2" chuck, low RPM Harbor Freight drill that is $50 on their website.  Please don't pay $50!  With about 30 seconds of time, you can easily find a 20% off coupon! If you have trouble finding one, shoot me a quick message. I always have one lying around.

The specific model for this drill is item#93632 but they update the number quite often.

NOTE: The auxiliary (front) handle is removable and you utilize the holes in the drill casing to mount the drill (using M10-40mm bolts).

The Base

The Base

The base was made using a stock piece of lumber from my local big-box hardware store. 

The final measurements of the base are:
Length: 24"
Width: 9 1/2"


I'll do my best to explain this part, but some of the build process was just "eyeballing" the measurements. 

The vertical piece on the right of the base is the drill mount.  The height of the drill mount is determined by the dimensions of your flywheel: Your flywheel needs to clear your base in order for your machine to work properly.

The vertical piece on the lower left is the linear slide mount. 

The Flywheel

The Flywheel

I wanted a more "organic" look to compliment the machine, so I made the flywheel from a piece of 3/4" thick oak board.  I figure the oak will hold up given the hardness of the wood.

To make this piece, you simple start with a center-point.  Using that point, use a compass to make a circle.  I made a 8 3/4" circle so I could have an 8" stroke on the machine. 

After that, you need to plot out the holes determining the stroke length.  To do this, simply measure out from the center. A hole 1" from the center will result in a 2" stroke, a hole 1 1/2" from the center will result in a 3" stroke, etc. 


From a design standpoint, you want to plot these holes on some kind of smooth arc. You can use a french curve to get the right design, or even the outline of a 5-gallon bucket will work. You just don't want the holes in a straight line...

On the back of the flywheel, I counter-bored the holes to accommodate the male end of my ball-joint linkage (the rod end wasn't long enough to make it through the 3/4" board

The center post of the flywheel is just a 1/4" bolt with a threaded hex standoff (available at a hardware store). 

The Rod Ends

Since I wanted to use a simple aluminum rod (purchased at the local hardware store) for my machine, I needed to make something to adapt the threaded rod.  I also wanted to avoid buying anything else... 

Here is what I came up with... I used the remaining Delrin to make a simple pivot joint. It ins't pretty, but it is rock solid.

The Linear Guides

The linear guides were designed to work much like linear bearings but have the advantage of being more cost-effective. 

These guides were made from a  1.25'' x 2.25'' x 10.25'' block of a material called delrin.  Delrin, also called acetal, UHMW or polyacetal, is a hard machinable plastic that is resistant to wear and tear.  For slide components like this, it works very well.  I purchased the delrin off eBay for $11/shipped.

I cut the block of delrin into smaller pieces and drilled a 7/8" hole to accommodate the 3/4" aluminum shaft.   You will need to drill a larger hole that you need since the plastic heats with the drilling and then shrinks down a bit.  Having the extra 1/8" gives the clearance you need for smooth linear action. 

Here is a picture of the final set-up:

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