Copyright 2011. figNoggle Designs.
7x10, 7x12, 7x14 Mini-Lathe Information
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SIEG X2 MINI MILL
HOW-TO Make Acetal/Delrin Anti-Backlash
Nuts (And An Alternate Method Of Table Removal)
- CNC V1 - CNC V2
- STUFFMADE - REDUX
as we've mentioned in the acetal gib strip how-to, there are pros
and cons of using this material. however, we think that the pros outweigh
the cons. you may be wondering if the use of acetal impacts the ability to
mill materials such as aluminum and steel. no problems here.
we have already made how-to's
detailing the standard acetal nut that's simply tapped and installed with
a quality ACME lead screw for the X and Y axes.
now we go into the makings of an
anti-backlash version of the nut.
the primary challenge is not the
design of the nut since there are only a few principles that can be
applied to simply address the issue of backlash, rather it's the challenge
of making this type of nut to fit within the limited space of the
mini-mill and not diminish the travel of the table...
if you want to reduce backlash in your stock nuts, click here.
| the makings of the anti-backlash nut
| here's the first round of prototypes. the x axis has less space to work
with than the y so off-the-shelf nuts just won't work very well.
| here it is installed on the x-axis. the principle here is that the springs
offer preload to push apart the two nuts. the major problem here is
alignment and resulting torque creating not-so-nice binding thereby making
unnecessary accuracy errors and friction.
we also tested cam-type nuts
but there's so little material left that reliability of the nut would be
| either way, the nuts had to be adjustable without major removal of the
note that the y-axis nut is adjustable without removing
the assembly. this is very convenient so that you can adjust backlash
preload as you wish.
| here are some prototypes of the second round of designs.
and the winning
| KISS. "keep it simple stupid."
we knew this would work, but wanted to
make sure we didn't leave out any iterations that may be better based on
some of our design criteria.
it's essentially the "split nut" design.
the only foreseeable problem with this is that with a 8TPI thread
across 0.630" and a 1/16" slit through the nut, you only get ~4-5 threads
| here it is in the y-axis installed.
again, note that the "preload" is
adjustable without removing the table assembly.
(see the acetal gib strip?)
| the alternate method of table removal
| in the previous how-to of the ACME leadscrew and acetal nut, we described
the "traditional" method of table removal.
here's the other way. be
careful not to nick the dovetails!
in four steps:
step 1. undo the gib strip set screws and push the gib strip out of the
| step 2. (in this case the x-axis) pre-install the nut onto the leadscrew
and crank the handle until the nut is roughly situated in the middle of
| step 3. position the table at an angle to the base (again, be careful not
to nick the base/carriage) and making sure the nut is positioned in the
nut cavity.. lay the table down to the carriage
step 4. re-install the
gib strip, reset the set screws and adjust
| final thoughts...
| with acetal gib strips, acetal anti-backlash nuts, and acme leadscrews
adjusted, we're able to maintain repeatability of less than 0.001" and
backlash + lead accuracy of less than 0.004". not too bad considering the
materials cost is much less than even off-the-shelf ballscrews and nuts of
you may be wondering if this this still holds true when
machining metals.. the answer is yes. as an example, we used a 2-flute end
mill, 0.020" depth of cut (doc), 1000 rpm, 15 ipm, making a clamp base for use with
considering the cost of precision ballscrews and nuts (this can easily
be over $1,000 for the X and Y axes combined to guarantee no more than
0.0005" lead accuracy and "zero-backlash" - you still have the issue of
cramming the nuts in the mini-mill cavity!), the acetal/acme combination
is a very good performing upgrade that yields a pretty good "bang for the
plans and kits are now being
finalized and should be available shortly. thanks for your patience!
read about backlash and
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