Messages

1151

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

« on: June 19, 2009, 12:46:45 PM »

OK, I mounted the new, larger air cylinder, and new Bellevilles.  I am now absolutely convinced this WILL work.  It works just fine as-is, but I'm not able to get quite the "slip torque" I'm looking for on the toolholder.  I'm aiming for 30 foot-pounds, and I'm not at a bit over 20.  A new, longer lower plate and longer lever arm should easily get me there.  At 20 foot-pounds, it works great.  Apply the air, and the toolholder just falls out.  I would guess my 2000# drawbar tension estimate is definitely in the right ballpark.

Regards,
Ray L.

1152

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

« on: June 18, 2009, 12:06:53 AM »

Ya know, it just occurred to me, it's easy to calculate the maximum torque the spindle motor can exert on the tool, which can serve as a guide for how much torque I need to set the drawbar for.  Since I'm using a VFD, max torque should be at base speed, in the lowest gear, which is 660 RPM.  The motor is 3HP, so the torque is roughly 3 * 5252 / 660 = 24 foot-pounds.  So, the 30 foot-pounds I've been aiming for seems like a reasonable target.

Regards,
Ray L.

1153

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

« on: June 17, 2009, 10:30:12 PM »

I am running a full size bridgeport clone , 3hp , 10x54 and havent had any problems . I mostly work in aluminum though and rarely do any drilling with that machine so mine may not be a good comparison

The 6-800lb number for r-8 collet came from an articlle in HSM about various collets somewhere in the past 15 years , I have seen 600 lbs mentioned in a thread somewhere in the past also. I would guess your 2500+ lb number is probably more accurate . My manual list a torque on the drawbar of 15-20 lbs which calculates to over 3000lb of clamping force  for a 7/16x20 bolt

look forward to updates when your new parts arrive

Yeah, I started with 900 pounds, and it's scary how easily the tool will move with so little tension.  I just wish I had some direct means of measuring the tension, but I don't.  Estimating from the Belleville specs and deflections is the best I can do.

Regards,
Ray L.

1154

General Mach Discussion / Re: ATC/ Rapid changer by Hightechsystems?????????????

« on: June 17, 2009, 10:03:57 PM »

Fred Smith of IMService has shown one  of them running at the last Cabin Fever and NAMES shows. He was running a program that just kept changing tools, but it seemed to work OK. I think it is his unit shown on the videos links of link posted.

The holder is a simple plastic finger, you program the tool to slide into it, then lift the z. The finger grabs the bottom of the holder.

A finger that starts thin, and ends up thick, so it lifts the red release collar as the spindle slides into the holder.

Regards,
Ray L.

1155

General Mach Discussion / Re: ATC/ Rapid changer by Hightechsystems?????????????

« on: June 17, 2009, 08:42:08 PM »

Is any one useing the rapid changer from Hightechsystems? They have a vid for using it as an ATC and I was wondering how it works and how you set up mach to handle a tool change like that.
http://www.hightechsystemsllc.com/rapid_changer.html

Thanks for any help,
Nick

The basic mechanism is very similar to the quick-release on an air hose - you push up on the spring-loaded red collar, and several ball bearings are then free to move away from the "pull stud" at the top of the tool holder, allowing the toolholder to come out of the spindle.  It would be very possible to make that work with Mach3, with some custom M6 macros.  It's a pretty pricey system, though.

Regards,
Ray L.

1156

General Mach Discussion / Re: Limitations of PC Parrallel Port

« on: June 17, 2009, 07:24:48 PM »

SmoothStepper is about $150.  Go to www.warp9td.com

Regards,
Ray L.

1157

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

« on: June 17, 2009, 06:01:10 PM »

I was under the impression the tormach  holderfs/r8 setup only needed a few hundred pounds of upward pressure on the draw bar to be secure. we are running a washer stack that generates 800lbs on the mill and unlocking with a .2" stroke bimba 4" pancake cylinder , cylinder was less than $100 and I havent had a tool slip in the past couple of years of operation . I hadnt thought about the load being applied to the bearings when unlocking , I would imagine they are probably holding up OK but I am now wondering about the severe load on the ballscrew assembly on my quill . I like your idea of the locking mechanism to handle that load .

Please keep us posted on your progress. I am always fascinated by tool changers and related components.

What kind of machine are you running, and where did you get the 800 pound number?  What's interesting is NOBODY seems to know what appropriate drawbar tension is.  I asked Tormach tech support, and the response amounted to "Beats the hell out of us!  If you find out, please let us know!".  So, what I did was put a 1/2" tool in the collet, tightened as I usually do manually, then measured the torque required to make the tool slip in the collet - came out to about 30 foot pounds.  I then put the new drawbar in, and played with different stacks of bellevilles, and different amounts determined the drawbar tension was about 2000-2500 pounds, so that is what I'm aiming for.  The only place I've seen any numbers tossed around, it was on smaller machines, like X2s, which certainly can get by with a lot less than my knee mill.  The 2500 pounds is also in line with my initial esitmates, based on torquing the drawbar to 25 foot-pounds, which is what most of the impact-driver drawbars do.  I have seen figures for drawbar stretch (0.015"), but don't know how reliable those are.

I do know my current setup can apply about 1500 pounds, and that is NOT enough - I can make the tool slip pretty easily at that tension.

Yeah, 800# seems like an awful big static load to be putting on the bearings or the ballscrews....

Regards,
Ray L.

1158

General Mach Discussion / Re: Losing steps

« on: June 17, 2009, 01:26:02 PM »

Could be mid-band resonance, which is an inherent characteristic of stepper motors, and can be mitigated by using drivers that damp it out (i.e. - Geckos), or adding harmonic dampers to the axis.

Regards,
Ray L.

1159

General Mach Discussion / Re: Limitations of PC Parrallel Port

« on: June 17, 2009, 01:18:37 PM »

Just wondering what the realistic limitations are of pulse speed when using a pc parallel port. Will it run fine up to 100khz with a modern computer or will I have to limit Mach3 to something much lower?

*Some* PCs will work at 100kHz. Most seem happier at 45kHz.  If you want high step rates, you should consider a SmoothStepper, which will step up to 4MHz, and with MUCH more stable, jitter-free timing than the PP.

Regards,
Ray L.

1160

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

« on: June 17, 2009, 11:49:48 AM »

Ray LOOKS good.   Here is something to consider. The piece that holds UP on the spring pack, the lower plate with the finger that slides under the pack. THis will be tricky to get the spindle in the exact position so the lever can slide under the pack AND still not have any play. ANY PLAY will cause the spindle bearings to load up as the pack is compressed. You might want to consider a push me pull me type of compressor arrangement that floats and as it is compressed both sides of the PACK are compressed at the same time. AND it puts zero load on the drawbar.

Another thought when building a drawbar is the machines always use a long 30deg angle tool holder that does NOT require any of the force of holding in the toolholder to be used to HOLD the bit as well. (;-)

Just a thought, (;-) TP

Terry,

Not so.  Initial position is not at all critical.  It simply needs to move up enough that the drawbar contacts the plunger.  At that point, the latch plate is guaranteed to be clear, so it can slide into position easily, as the whole assembly floats.  There will be slack in there, by design.  The initial movement of the plunger will lift the assembly further until the latch plate contacts the underside of the flange under the Belleville stack.  It is impossible for any force to be transmitted to the spindle.  Further movement of the plunger will then compress the Bellevilles.  The only force that can be transmitted to the spindle is the initial downforce provided by the springs on the guide rods, which is strictly limited, and provided purely to pop the colet free of the taper (and to do so much more "gently" than whacking the drawbar with a mallet).

I would sure love to have a CAT30 spindle, but that ain't in the cards.  This design does appear quite capable of providing the same drawbar tension as hand-tightening, or using an impact driver, so should get the job done.  Hopefully, the new air cylinder and Bellevilles will show up today, and I can put it to the test....

Regards,
Ray L.