Re: [SherlineCNC] Re: EXTENDED X AXIS FROM A2ZCNC
- Hi Phil,
I originally had the same concerns about the A2Z X/Y tables, I went
ahead and got them anyway (with the Kerk screws). What I will say at the
start, this is no Sherline, although originally designed to fit the
existing Sherline saddle when you get it with the Kerk screws the new
saddle is massive compared to the stock one. although the distance
between the dovetails remain the same for compatibility with Sherline
the length on both the X and Y portions is longer (4.5" x 3.5") giving
much more support.
I normally use a tooling plate of 8" x 14" and have found no problems
utilizing up to its full capacity for milling operations, no evidence of
tool chatter when used at the extremes.
With the release of the Z axis, A2Z will I believe have a nice niche for
itself as an alternate mill, that can still utilize all the Sherline
>[Non-text portions of this message have been removed]
> Excellent reasoning. My problem with the Sherline table (aside from
> the fact
> that everything is too small) is that the ways are too narrow and the
> contact surfaces too short. When you move to the extreme ends of the Y
> travel the side play is multiplied proportional to the distance from the
> center of the slide, which tends to produce pretty bad chatter. I would
> think this problem would be amplified with your extended Y travel.
> This has
> been my hesitation up to now. If your base and slide were wider than the
> Sherline, and your table was wider (more than two slots) I probably would
> buy. Seems to me you're not far from offering a complete machine.
> Phil Mattison
> http://www.ohmikron.com/ <http://www.ohmikron.com/>
> > David,
> > The reasoning is that most people use stepper motors on their Sherline
> > CNC machines and stepper have a sharp fall off of torque as the motor
> > speed hits the point where the inductance starts to limit the torque.
> > With a 20 tpi screw that torque fall off occurs at a rather low speed.
> > Due to this issue people try to increase their stepper based systems
> > performance by either increasing the voltage the steppers run at to
> > overcome the inductance and move the fall off of torque to a higher
> > value or they try to do it by putting on larger motors to get more
> > torque but then run into the issue that larger motors have higher
> > inductance so it fall off occurs at a lower speed. My thinking was that
> > most people are running microstep systems so the the actual movement
> > per step with a 20 tpi screw is actually well below the mechanical
> > ability of the machine to make that small movement. So I figured if I
> > could slow the motor speeds down the torque would increase greatly and
> > the per step movement increment would become closer to what the machine
> > could actually resolve. Plus the more course pitch screws are far more
> > efficient at transmitting the torque then the fine pitch screws. So
> > over all the rapid speed and top reliable cutting speeds would increase
> > greatly and the resolution would not be effected.
> > Testing and customer feedback all confirm that the theory is true. With
> > the 4 tpi dual lead screws and 230 oz in motors I have reliable 100 ipm
> > rapids and cutting speeds using Mach2 and a Xylotex based controller.
> > Plus the precision is actually increased compared to the 20 tpi screws
> > due to the low and non-changing backlash of the Kerk self compensating
> > nuts.
> > Tim
> > A2Z Corp
> > A2Z CNC division
> > 1530 W Tufts Ave Unit B
> > Englewood CO 80110
> > www.A2ZCNC.com
- Hi, thanks for the information.
Is there some kind of way to adjust the gib tightness to be "perfect"?
The method i'm using currently is just using approximation to ensure
that the table slides smoothly and has minimal freeplay.
Is there a better method or a right method?
> --- In SherlineCNC@yahoogroups.com
> <mailto:SherlineCNC%40yahoogroups.com>, Chye NW <chyenw@...> wrote:
> > Thanks for the info. I read that some of the people have problem with
> > gibs, do i need some special or longer gibs for it?
> The issue is that very rarely the gib that came with the machine
> originally was trimmed at the other extreme from what is needed for the
> new parts. This is exactly the same as when you put on our extended
> table or Y base without the precision leadscrew upgrade.
> As an example, if the original saddle was on the narrow end of the
> factory tolerance and the table is on the wide end then the gib is
> trimmed so the thinner part is cut off. Now if our saddle is on the
> wide side of the tolerance and the table on the narrow side it will
> need the thinner end of the gib that was cut off when it was installed.
> Fortunately, both Sherline and A2Z aim for the middle of the tolerance
> range so there is usually enough adjustment in the gib to be able to
> use the original one. Very rarely does the gib need to be replaced with
> a new one so you have the full length. Then you cut off the part you
> don't need. If you find your gib to be too loose, you can just put a
> shim between the gib and the saddle and that takes up the excess space.
> If you need the gib to be thinner (very very rare) you can just use
> sone coarse sandpaper on a flat surface to make the gib thinner.
> A .001 - .002" chance makes a major difference in the fit.
> Hope this all makes sense?
> A2Z Corp
> A2Z CNC division
> 1530 W Tufts Ave Unit B
> Englewood CO 80110