Messages

1161

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 17, 2009, 10:34:22 AM »

looks really neat .

Have you thought of just using a 4" bore pancake cylinder supported over the end of the factory drawbar?

Considered it, but it wouldn't get the job done.  At 100 PSI, a 4" cylinder would be only about 1200#.  I need at least twice that.  Plus, it would have too much travel.  I only need a total of about 0.100".

Regards,
Ray L.

1162

General Mach Discussion / Re: motor tuning: aim for max speed??

« on: June 16, 2009, 06:07:00 PM »

Thanks for your reaction Hood,

But is a high speed necessary for certain turning jobs?
Or can all parts be made with a much slower speed? (keep in mind that I'm an absolute beginner)

If you're an "absolute beginner", then tune everything WAY down, or you'll waste a lot of money replacing broken tools (or broken machines) until you learn how to operate it properly.  It is VERY easy with CNC to make a simple mistake (like type + instead or - or X instead of Y), and causing the machine to do something stupid.  The faster the machine, the less chance you have to say "Oh, s**t!", and stop it before it crashes.

Regards,
Ray L.

1163

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: June 16, 2009, 04:42:00 PM »

Here is it . . . will be avail in HD after YouTube is finished processing, but is viewable now.

http://www.youtube.com/watch?v=NzY-OqckqpI

Special thanks to Hood for the re-homing info.  Also Vmax, RayL, Machinemaster, and others . . . 

BTW, lots of light cuts this go round. I will have a lot more power once I get the Viper drive (delayed waiting on parts  )  With the 1800 line encoder, the Gecko faults with a normal cut.

That is seriously cool!  I hope to do something similar someday, if I ever finish my toolchanger....  I've got some simple parts I sell that could be done very easily like that.

Regards,
Ray L.

1164

Show"N"Tell ( Your Machines) / What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 16, 2009, 04:27:58 PM »

I'm in the process of adding a toolchanger to my BP clone mill.  First step is a power drawbar.  Rather than use the very common impact wrench approach, I wanted something that would leave the collet in place, and simply pop out the tool.  I will be using Tormach TTS toolholders.  So, taking a page from the design of many VMCs, I've created a design that tensions the drawbar using a stack of Belleville washers.  The drawbar is initially tensioned in the normal manner, by tightening with a wrench, to compress the Belleviille washers enough to create the desired drawbar tension (about 2000 pounds, as it turns out...).  To release the tool, all that's required is to compress the Bellevilles a bit further, then push the drawbar down to pop the collet free of the taper, and the tool simply falls out.  The trick is to provide a means of compressing the Bellevilles that does not place that 2000+ pound load on the spindle bearings.  To accomplish that, a small arm is rotated in under the Bellevilles, to take the downward load.

Since, on my first attempt at this, I was largely shooting in the dark as far as the required forces, and some of the other side-effects of the design, I've found I need to make a few minor modifications to the design to get it working properly.  But, the first attempt, shown in the below pictures, does, in fact, work pretty well.  The biggest problem is I under-estimated the drawbar tension required, and the air cylinder in the pictures is not quite up to the task.  A larger cylinder will be here in a day or two, which should do the job nicely.  The other "gotcha" is that the long drawbar extension sticking up above the head "whips" at speed - not good.  So, it will be surrounded by a cylindrical guide, rigidly attached to the spindle, that will rotate with the spindle and prevent any whipping.

The assembly is fastened to the head, by bolting an adaptor ring to the flange that retains the upper bearing outer race.  The upper bearing inner race retainer is replace with the drawbar guide tube.  The adaptor has two guide rods rigidly attached.  The rest of the assembly "floats" on these guide rods.  The guide rods have concentric springs on them such that the whole floating assembly is spring-loaded downward.  To do a toolchange, the quill is run fully up, which causes the top of the drawbar to contact the plunger in the center top of the drawbar assembly.  This compresses the springs, placing a downward force on the drawbar assembly.  This is the force that is used to pop the collet free, and will probably be on the order of 100 pounds - hardly enough to harm the spindle bearings.  A small air cylinder then flips an arm in under the flange that lsupports the bottom of the stack of Belleville washers on the drawbar.  Once that arm is in position, the large air cylinder is activated, which compresses the Bellevilles between that arm, and the plunger.  Since the whole assembly is floating on the guide rods, none of the Belleville force is transmitted to the spindle - only the initial downforce of the springs on the guide rods is transmitted to the spindle.  Once the Bellevilles are compressed sufficiently (0.030-0.050"), the collet pops free of the taper, and the tool falls out.  Once the new tool is installed, the air pressure is removed from both cylinders, and the collet is once again locked by the tension in the Bellevilles.

This is a totally bolt-on design, which requires absolutely no modifications whatsoever to the machine.  Drawbar tension can be adjusted over a very wide range by simply changing the number and type of Belleville washers used, and, if necessary, the strength of the air cylinder.  Collet-popping force is adjustable by adjusting the pre-load on the downforce springs.  Initial position is set by simply adjusting the length of the link on the air cylinder.  All very simple and flexible.  Tool changes become almost instantaneous - literally less than a second to engage or disengage the drawbar.

For the toolchanger, I am taking a very simple route, since I only need a few tools - I will have a single-row rack of tools mounted to the T-slot along the front face of the table, holding perhaps 8-10 tools, or perhaps 4-6 tool racks mounted at either end of the table.  The tool pick-and-place will be handled entirely by moving the machine, with no additional mechanism required.  This does cost a small amount of useable table travel, but since I have a 49" table with 34" of travel, I am more than happy to lose a few inches of workspace in exchange for the huge increase in productivity I'll get from the toolchanger.

Regards,
Ray L.

1165

General Mach Discussion / Re: can somebody help me plug in my shuttle pro 2

« on: June 14, 2009, 11:05:49 AM »

thanks Hood.
i got my shuttle to work so far and I must say it works pretty good.
so know that I label some of my buttons ,
can some one explain how can I make this shuttle work so that my (Laser  X AND Y axis zero ) work,  I would like to make the bottom lower right button work for that macro.
and also I would like to make the (Z axis tool zero) work,  and I would like to make the bottom lower left hand button work for that macro.
 i dont know how to make this work.
any help would be epprreciated
thanks.

The buttons are assigned by going to Config->ConfigPlug-Ins, then click on the yellow "CONFIG" next to the ShuttlePro.

Regards,
Ray L.

1166

General Mach Discussion / Re: parallel port

« on: June 13, 2009, 08:22:17 PM »

The step pulses are generated by software, in a very low-level driver.  Anything in the system that loads the CPU, or the memory busses, can prevent that driver from issuing the pulses exactly when it should.  Video drivers, network drivers, and other high-bandwidth devices can do this.  On-board graphics controllers can be particularly bad, since they generally keep the frame buffer in main memory, so can significanrly increase latency of CPU accesses to memory.  Get the Windows optimization instructions from the Artsoft website.  That will give you a good idea the kinds of things that can affect pulse stability.

Regards,
Ray L.

1167

General Mach Discussion / Re: How do I reverse the values on my DRO?

« on: June 11, 2009, 09:44:56 PM »

Simple question. I forget how to get the DRO to change my axes values. Z up used to be Z- and down used to be Z+. How do I get the DRO to read reverse so I don't have to change all my programs?  Thank you for all your help.    Corey

Just change the polarity of the axis DIR outputs.

Regards,
Ray L.

1168

General Mach Discussion / Re: Is this backlash or missed steps????

« on: June 11, 2009, 11:32:09 AM »

simpson36,
I never tried putting a some long value into the steps per unit, but you may want to try and then use the xmll reader to see what value is stored in the xml and if it takes it.
What does the manual say?
RICH
 

It appears Mach saves 6 only decimal places in the XML.

Regards,
Ray L.

1169

General Mach Discussion / Re: Is this backlash or missed steps????

« on: June 10, 2009, 04:51:50 PM »

I am still a noobie so forgive my ignorance but why would those numbers not be pretty. If i multiply those by the microstepping of the geckos i would get 1551.76 for X and 1637.70 for Y.

Yes, if you're willing to ignore all those other digits, which will lead to position errors on long moves (many steps).  On a small machine, or short moves, it won't matter.

Regards,
Ray L.

1170

General Mach Discussion / Re: Is this backlash or missed steps????

« on: June 10, 2009, 04:17:36 PM »

I am a bit at odds with Ray - this might be because we see your set up differently.

I see it as the motor drives the gearing. (why you didn't use simple numbers for this I don't know - I use 3 to 1 timing belts) the gearing drives a 40 tooth pinion which sits on a rack of 0.2 pitch. You do not say whether this is mm or inches, but it does not matter.

With this set up, every turn of the 40 tooth gear means 8 units of movement.

Both axis -  200 (motor steps per rev) x 10 (microsteps - 10 for gecko - alter this to whatever you are using) = 2000.
Pinion on rack - divide by 8 = 250 steps per unit.
Multiply this by 4.875 for X axis = 1218.75 steps per unit.
Multiply this by 5.143 for Y axis = 1285.75 steps per unit.

This needs amending for the microstep function - may be to 8 or 16 whichever your drives use but I think it is accurate.You will notice, of course, that the steps per unit are not whole numbers, and this is becasue of your odd gearing, It doesn't make much difference in the scheme of things, becasue Mach calculates to 12 places of decimal - but for working these things out a simple 5 to 1 would have been easier, or even a 4 to 1 to offset the pinion. Are these numbers anywhere near what you have been using.

Where do you get 0.2 pitch from?  Actually, I think it's even worse.... He describes the gearing as "40 tooth 2.0 pitch diameter pinion gears on racks".  If I'm interpreting that right, these are 40 tooth gears with a pitch diameter of 2".  The # of teeth is really irrelevent here.  What matters is that one rotation of the gear will move the rack 2" * PI or 6.283185307179586476925286766559", where my calculation assumed it would be 2".  So, I now get:

X Axis: 200 * 4.875 * 1/6.14 = 155.1760695145979523746616692882 steps/inch
Y axis: 200 * 5.143 * 1/6.14 = 163.70677446432354237187383900497 steps/inch

Not pretty numbers!

Regards,
Ray L.