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7x10, 7x12, 7x14 Mini-Lathe Information
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FREQUENTLY ASKED QUESTIONS
RE: FINDING THE RIGHT SIZE TIMING BELT
Q. What size belt should I use if I know the two pitch diameters of the pulleys
and the center to center distance between them?
A. Use our timing belt calculator. Works for MXL, XL,
and L sized belts.
RE: MACH "STEPS PER INCH"
Q. How do I setup the "steps per inch" numbers so that I can get the X, Y, Z
A. Use our Mach "Steps per unit" calculator. Currently works for screw and nut setups only. Other setups coming soon.
RE: DRILLING NICE HOLES
Q. My drill bit keeps wandering and my holes are "off". What do I do?
A. Use the following (in this order): 1. transfer punch to locate the hole 2.
center punch to make an indent 3. use a center drill 4. use a machine screw
drill bit (these are stiffer and shorter than jobber bits) or undersize the bit
and then use a reamer to get a nicely rounded hole.
RE: SAVING MACHINING TIME FOR IDENTICAL
Q. I have two identical pieces to machine. How do I save time?
A. Use a piece of paper or index card (thicker than paper) to allow for that
thousandth difference between the two pieces. Mount in vise. You can also use
clamps (such as the Kant-Twist) brand (excellent!) to hold the two pieces
together while in the vise, then when you remove them for another operation (say
you flipped them around).
RE: TRAMMING THE MILL
Q. I just bought the mini-mill. How do I make sure it's square to the table?
A. Click here
Q. I just bought the lathe and/or mill. What tools should I buy?
A. Click here
RE: BACKLASH AND LEAD SCREW ACCURACY
Q. How come whenever I turn the handwheel the other direction there's play
and slop before the table/carriage finally engages and moves?
A. This is backlash (aka "axial lash" or "lash") - the axial gap between the
screw thread and nut thread. This translates to (in a rotation to linear motion
scenario) additional rotations of the screw before the nut and screw engage
positively. In a manual machine and coupled with a DRO (digital readout) to
determine table position, backlash can be annoying, but is not much of an issue
since you no longer have to keep track of handwheel turns and re-zeroing, etc.
In a CNC system (computer numerically controlled), backlash is of huge
importance. What is sometimes forgotten however is the lead screw accuracy when
overall machine accuracy is considered in a CNC machine. Here's why: even if you
have a zero-backlash system with the use of some form of anti-backlash nut, this
only means that reverse rotations from one direction to its reverse axial
direction won't include any additional rotation causing more machine positional
error. However, perhaps you have a leadscrew with lead accuracy of 0.004 in./ft.
(this means that the leadscrew could be off by as much as .004" by the end of a
12" travel), this translates to 11.996" of travel with full error.
Imagine this combined WITH backlash!. In order to get a truly accurate system
you'll need both a highly accurate leadscrew (or ballscrew) and some way of
addressing backlash at the mechanical level (not the software level - i.e.
backlash compensation). Perhaps the most important question to ask is HOW
accurate you want the machine to be? If you're making wooden parts with
tolerances of +/-0.05", almost any CNC system can accommodate. If you want to
get to +/-0.001", you'll have a lot to work on. Click here to read more on this
RE: ER SPRING COLLETS, R8 COLLETS, AND
Q. I've heard about these "er collets" or "er spring collets". What are they
and how do I use them?
A. Let's start with the basics. Collets are used to hold cutting tools. There
many different types ranging from your most basic of R8, 5C whereby each
diameter requires its own sized collet to spring collets whereby they grip
ranges of diameters for each size of collet. In a Z-axis limited machine such as
the mini and small mills, the use of a drill chuck can reduce travel by 2" or
more. This is a huge advantage of using a spring collet. Since the spring
collets can grip drill bits of most common sizes ranging from ~1/8" to ~1"
shanks (they usually have .040" of gripping range for each size collet), you no longer need to use a drill chuck. Plus, even the inexpensive
import er collets usually offer 0.0006" concentricity. With ER collets
alone, you have a handful of sizes to choose from ranging from ER-11 to ER-50.
Each of these numbers indicate the range of holding they accommodate. For
example, an ER-32 size has a gripping range of .080"-.787". But before you go
off buying er collets or other types of spring collets, it's a good idea to know
the different types of spring collets. Click here to read more on this topic.
Looking for mini-mill help and how-tos? How about lathe help and how-tos?We're prototyping a benchtop CNC vertical mill using the DigiSpeed-XL interface card for Mach, Dart Controls and KB Electronics KBIC/KBMM 90VDC motor controllers, 1.5HP treadmill motor from Surplus Center and a R8-spindle head from the X2 mini-mill - not to mention Gecko servo drives and an entirely closed-loop system. Come take a look!
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