How to make a mini milling machine- manual or CNC!

Step 2 Design

This mill was designed so that it could be converted to CNC by adding stepper motors and motor mounts in order to make it as versatile as possible. If you only want to mount stepper motors and do not have the need for manual operation then feel free to modify it accordingly.

The design uses an anti backlash system. Backlash is when you turn the handle forward and back and the cross slide doesn't move- it's the bane of many a machinist and it makes it hard to make accurate cuts because you have to compensate for it. It's a bit trickier to build the mill this way compared to using a single ACME nut but it does work very well and it's worth the effort required.

I primarily used Birch plywood and MDF for the construction because it's stable, flat and it works well in this application (it's also what I happened to have on hand!) There are several parts that have wood dowel inserts- this is because when screwing into the end grain of plywood it doesn't hold screws very well at all (ditto for MDF.) The slides are made from Delrin because it works well in this application, it's easy to cut and it holds screws well. I wanted to construct this using materials that could be purchased at local hardware stores. There are a few areas where it can be built differently and I'll note them as I go along.

Here's some sketches of the most critical parts as well as an exploded assembly drawing- the drawing should be used as a general assembly aid (a lot of the bolts are left out of the drawing for clarity.) Many of these dimensions can be modified to suit the parts and materials you might have available. The most important thing is to make everything as absolutely square, straight and flat as possible.

Comments

[blue_hound]

I see the acem nut is only retained on one side. Is it necessary to make a retainer for the spring side or does the spring tension keep it in tune? thanks in advance.

[Honus]

The spring tension keeps in place- it can't rotate in the slot.

[maxxdamage]

Can you please tell me more about why you need the anti backlash system and what makes the backlash appear ? is it because you used two bolt nuts?

[Honus]

Backlash occurs due to slop in the threaded nut drive system. When the threaded rod turns the nut will take time to load and actually move- you can turn the rod a fair bit without the nut moving. This causes a lot of problems with positional accuracy. By using two nuts with a spring you are effectively pre loading the drive nut and reducing the amount of slop in the drive system. There are other ways to accomplish this- a Delrin nut works well (which is cheap) as do ballscrews (which are very expensive.)

[maxxdamage]

Thanks man! it helped. I did a project for my school based on this model. It was one of the best in my class. A+ Thanks for sharing! you are a pro. http://picasaweb.google.com/catalin.art/ProiectLicenta#

[Honus]

That is so awesome!!

[mactard]

Looks like someone took a drafting class or two. Wow great sketches.

[off_white]

 Wow, that "quickie sketch" is extremely precise and elaborate. Good job! It's nice seeing hand drawings for once.