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Step 5: Make the anti backlash screw blocks

Picture of Make the anti backlash screw blocks
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Take the three pieces of 2 1/2" x 1 7/8" plywood (you could also use Delrin or MDF) and cut them according to the drawing. Drill and counterbore the holes for the mounting bolts. Drill and tap the 1/4" Aluminum rod for the 4mm bolts and insert them into the blocks (make sure you can see the threaded holes.) If you use Delrin to make the parts you can skip the Aluminum inserts and just thread the holes in the blocks for the 4mm bolts that hold the metal plate that retains the ACME nut.

My blocks were cut by hand- and it shows! The best way to cut the 1/2" wide slots for the ACME nuts is to make a jig and cut them using the router table. Clamp the screw blocks in the jig and then run the jig over the router bit to cut the slot. Don't try to cut the slot to full depth in one pass- just slowly increase the bit height and make multiple cuts until you get the desired depth. Cut the slot for the non spring side first and then flip the piece over to cut the other slot- that way both of the ACME nuts are guaranteed to be in perfect alignment.

Now make some 3/4" x 1 7/8" retaining plates for the front by drilling holes for the mounting bolts and a 5/16" hole so the ACME rod can slide through.

Check the fit of the parts by assembling it as shown in the drawing. The spring should be 1 1/4" long ( or close to that) before being compressed.
 
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where do you put the 1/4" aluminum rod in these???? (thread-less)
Honus (author)  Flying_MashedPotatoes4 years ago
The Aluminum rod is used in the anti backlash blocks. They are there to make sure you have something solid to hold down the 4mm screws that hold the retaining plate on the front of the block.
madmaze4 years ago
I was wondering what "anti-backlash" exactly refers to? I am by no means a Mech Eng. but If you could please what the problem is this is solving?
I assume that the sping gives it a little bit of play, but what happens if the spring wasnt there?
madmaze madmaze4 years ago
never mind i understand it now, it has to do with the way the threads of the leadscrew mate with the threads of the nut.
more info:
http://www.cncroutersource.com/back-lash.html

how powerful of a spring is in there?
Honus (author)  madmaze4 years ago
I honestly don't know. They don't need to be super strong to do the job- if the spring rate is too high it can cause some binding in the lead screw. I just picked them up at a local hardware store.


madmaze Honus4 years ago
hmm i guess im just gunna hafta see what i can find =)
my suggestion is you hit up CNC zone for questions on all of this. there are a lot of really nice people there that will do more than you can imagine to help out others in this hobby.