After 2 weeks, and a few switches, I'm Done!

[musicmkr]

With the day off yesterday, I had a chance to finish wiring up my machine, and give it a try. It took a total of two hours to crimp all the plug connections, wire up the Xylotex, and hook up the power supply.

Once the motors started humming I thought I was done, but that was just the beginning. It took longer to work out the bugs than I thought but by 6 pm I was milling like crazy.

I did a few things that are not ususally done to build these machines, so I thought I would point them out to help any other people who want to build a dirt cheap machine.

1. I used 1/4-20 lead screw, and didn't trun down the ends to fit in bearings. Instead I just cut them to length, and got .25 id ball bearings.

2. First I tried using a timing belt to run all axis' lead screws, but that turned out to be more work than necessary. 1/4-20 rod is flexible enough to make up for any shaft mis-alignment, simply hard couple the motor shaft to the lead screw and call it a day.

3. I tried loading two nuts against the bearing at either end of the screw to keep it form moving in the axial direction. This isn't necessary when you hard couple the screw to the motor shaft.

4. I didn't bother with linear bearings or anything like that. I simply used 3/8 thompson rod, and drilled 3/8" dia holes through my axis supports.

5. I used cheap steppers from allelectronics.com.

6. Cooking oil is an excellent oil for lead screws and slide rails, allthough the first time your wife finds aluminum chips in her cooking oil you will have to get your own bottle.

[ger21]

3. You're machine looks pretty small. On larger machines this could damage the motors.

6. Doesn't that stuff get thick and sticky after awhile?

[Albigger]

Looks good, nice machine.

I have a couple of questions, as I am starting construction on my first cheap machine to learn the basics.

How is that dremel mount working out? Any noticeable play? (I have the same model dremel)

What material did you use for the machine frame/base? Have any more pictures of it?


It seems there would be a good amount of play between your drilled 3/8" holes and the thompson rod, is this so or does it fit pretty snugly? I could see maybe reaming a hole, but drilling sometimes leaves oversized holes that would be undesireable.

How did you couple the leadscrews to the motor?

EDIT: and I agree with ger about the cooking oil, I would get something else on there because it will get sticky after a while.

[musicmkr]

ger21,

you're right about the motor, I should have clarified. After all my project was to build a cheap machine, anything larger that this would be more expensive. And I havn't had a problem with the oil gumming up, but I'll let you know if I do.

Albigger,

The dremel sucks to mount. There are only two sections that are round, so you have to use those. I found that i could get it to sit much better by taking off the screw on plastic piece at the spindle end. This leaves exposed threads, that fit nice and snug in a hole of appropriate diameter. For the top I used the dremel to make a slightly oversized hole (1.9" ?? maybe) and I cut out some plastic wedge pieces that I use to center the tool and hold it tight. They work great for machining, and also function to save your bit/dremel in you drive the Z down into the piece, by releasing the tool instead of breaking the bit. (It takes quite a bit of force to release the tool, but it prevents damage)

The machine is made of 2"x4"x1/8" aluminum tube, and the tables/slides are made of 1" thick High Density Polyethylene.

As for setting the thompson rod, I drilled a hole that was slightly undersized, and then using the dremel cut relief notches out to 3/8" dia at the quandrant points on the circle. Then smacked the rod in with a hammer. As long as your holes and notches are accurate then the rod will center nicely. My machine doesn't have a problem with binding at all. Now that I have a milling machine of sorts I would have made adjustable rod mounts, but at the time a hand drill and dremel was all I had.

To couple the rod to the motor I used a rigid aluminum couple with two set screws from mcmaster. Ger21 is right and if you're making a larger machine then you'll want to load the rod against the bearings to avoid axially loading the motor, but my machine is so small that it doesn't matter.

As for pictures I'll try to upload some to a member gallery.

[Bloy2004]

Your "cut-corners" approach is great! It does what you want/need it to do. I'm just curious about the machine being able to withstand the test of time/usage. It might be a good idea to log the hours of operation to determine (for others) how long the machine can maintain its present accuracy before overhaul. The nice thing about your machine is that when wear compromises your needed tolerances, you will be able to easily/cheaply "renew" it. Your machine is an exellent example of getting a "working" device up in a hurry and on a budget.
Bloy

[whiteriver]

How about more pictures. I think this might be a good cheap design for school kids. It looks simple enough and the materials must be cheap. How much total into the project. Could you break it down into hardware and electronics. What is your working envelope? What size steppers?
I wonder if one could put oil impregnated bronze bushings into the poly where it slides on the rods. Would that increase the life and help keep the cooking oil to a minimum. You could make the bushings on a drill press if you didn't have a lathe. Even could turn them down smaller if needed on a press. I think the solid rod is pretty cheap or get some from Reid tool supply or Mcmaster Carr.
I like it when people improvise and make a neat little machine for not much money. Very cool. thanks for the post.

Donny

[samualt]

That is a great design! You should write something of a how-to for those building small inexpensive machines. Kudo's!

Seriously though, I wouldn't use cooking oil. It's organic and might even make food for certain types of bacteria, which would make it thick and cloudy looking. It will also get stiff in cold climates, and over time. I have used it on high-voltage capacitors and found it's not good for some rubber and plastics, it made them soft and gooey after a few months.

What you are looking for is a nice bottle of gun oil. It's cheap, made for machines, and as far as I know won't hurt plastics. Or, just get some "3-in-1 oil" at the hardware store. It's about the same thing.

[whiteriver]

I have a cement mixer I picked up at Lowes last year and it comes with a bottle of vegatable oil for the gear. Its all they recommend for it.

Donny

[musicmkr]

Thanks for all the comments. I had thought about putting together a set of documents, a sort of "how to" for building a similar machine. First I'll see how long this machine can run trouble free.

As far as the cost brakedown goes, Here's what it would cost to build another one like this. I should note that I did get the aluminum for free from the scrap bin at work, but I'll give the price you could expect to pay retail.

Aluminum tube (10 ft) Approx $60
Aluminum Angle (2 ft) Approx $15
3 Motors (allelectronics.com) $45
12x24x1 HDPE sheet approx $25

Thompson Rods, Lead Screws,
fasteners, 6 flanged bearings,
3 shaft couplings, & misc Approx $125

Total for Machine $270


Plus add controllers and software.
I used a Xylotex 3 axis $125
Plus Mach2 $150

My working area is 8"x7"x3.5". On this machine the 3.5" doesn't go down to the table because the work I do requires additional fixtures, so I didn't want to waste Z travel area. The good news is that the same travel, down to the table would make the machine 2" shorter.

Ill post more pictures later.

[musicmkr]

Engravable Plastic Sign

[musicmkr]