In response to a comment posted by Will O'Brien in the Engadget CNC thread, we've decided to start a competition to see who can build the best homebrew CNC machine for less than (or equal to) US$70.

This competition is to build the machine only, not including motors, controller, computer, and software.

Pricing:

Freebies and On-Hand Materials:
All materials that are used to build the machine must be priced, even if these materials or parts were given as freebies or happened to be on hand. For example, if you uses parts out of an old printer you would have to list the price as what one would reasonably expect to spend to buy the printer from some place like eBay or a used electronics store. This also applies to screws, glue, lumber, etc. The purposed of this is to insure that the machines could be replicated by other people who might not have the same components (old printers, etc.) on hand or able to get them as freebies.

Taxes and Shipping:
Sales tax will not be included in the $70 budget due to the fact that the location of the contestants will most likely result in variations in local tax rates.
Whether or not to include shipping charges from Internet purchase must be decided by the contestants.

Tools:

The use of any lathes and milling machines (CNC or otherwise) for building these homebrew machines is prohibited. However, once partially built the CNC machines can be used to make their own parts (not exactly sure how, but just in case).
The use of table saws, drill presses, and any hand-held power tools is allowed (basically anything that isn't a milling machine or lathe).

Scoring:

Machines will be scored in three major areas: cutting area, rigidity, precision, and price. Speed will not be counted since that is more dependent of the motors and controller than machine design.

Images and/or video will be required to prove each area of scoring.

Cutting Area:
the score for cutting area shall be calculated my multiplying the total travel of the X-axis (in inches) and the travel of the Y-axis and the travel of the Z-axis.
Formula: Cutting Area Score = [X-axis]*[Y-axis]*[Z-axis]

Rigidity:
1 point shall be awarded if the machine can mill foam.
2 points shall be awarded if the machine can etch a PCB.
4 points shall be awarded if the machine can mill wood (any type except balsa)
8 points shall be awarded if the machine can mill plastic (PVC, Lexan, etc)
16 points shall be awarded if the machine can mill Aluminum and/or Copper

“Mill” means the machine must be able to take a plunge cut with a 1/8” or larger end mill. Note: the collet on most Dremel-type tools is 1/8”.

Precision:
The machine must be able to engrave either the Hack-a-Day skull and cross-hacks logo or the Engadget “E” logo (competitor's choice) onto a penny in the area under the Lincoln Monument.
4 points if the logo is 1/8” or shorter
8 points if 1/16” or shorter
16 points if 1/32” or shorter

Price:
1 point shall be awarded for every $2 a contestant does not spend from the original $70.




Questions? Comments? We need to decide if we want to include shipping.

oooh, I'm excited.

It sounds good to me, except I think 1 point per 10 cents saved it a little high and would put too much importance on making it with very little money instead of making it very high quality.
So I would propose that it would be changed to 1 point per 2 dollars saved, so those points are more of a bonus as opposed to a majority of the points.

Good point, I'll change that.

BTW, we haven't heard from Will yet, anyone know how to contact him to make sure he knows about this?

Since he's from engadget you might wanna post over there.

Thanks, I think the rules look good now.
Maybe submit it to the HaD tipline.

That penny thing sounds pretty impossible...

When you say that it is to make the machine not the motors and electronics and stuff. Does that mean we don't hook up motors and stuff to it? Or is it that the motors don't count for the money value?

Right, the machines will use motors and controllers (unless someone can figure out a way to make a machine move without them) but they will not be part of the $70 budget.

The main reason is because all the motors and controller really have an effect on as far as performance is speed, all other aspects such as accuracy, cutting area, and rigidity are governed by the design of the machine.

Besides, it would be very difficult to build a decent motor/controller/power-supply system for less than $70. For example, the engadget machine used the UCN5804B IC as the main chip for each axis of their controller. These chips cost $8.50 each at alltronics.com, so three of them (one for each axis) would run you $25.50 not including tax or shipping, that's more than 36% of you total budget gone and you don't even have the rest of the components for the board, the motors, or the power supply.

I think I can make the table with no problem, but the hard part for me will be trying to interface with the motors and have a computer control it all.

A really great CNC machine can be built for under $100. You can use roller blade bearings for the end bearing of the threaded rod. Use black auto vacuum line to join the stepper to the threaded rod. A 1-1/4" piece is all you need per motor. If you clean the motor shaft and threaded rod the vacuum line will fit very tight. It gets tighter with time. Clear tubing BLOWS!

Buy your 1/4-20 threaded rod and drill rod at a machine shop supplier. The threaded rod comes oiled not plated. The drill rod is straight round and polished. These items will also be cheaper and of better quality than that found at home centers. Grey PVC works better than UHMW or HDPE for the body of the machine. You can get it at most plastic centers. For the beginner I suggest you use pads of plastic to ride on the round shaft. This removes the binding problem you will have with bushings. The pads can also be adjusted in to remove unwanted play. The linear bearing needs to be softer than the rod it is riding on.

The solid rods that are found at home centers are not round or straight. The are called Cold Rolled Steel. Some people smoke screen them by calling them "CRS" Lipstick on a PIG!

Cranky

Father of cheap CNC