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  #151  
Old Sun 01 November 2009, 09:14
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I havn't looked at this thread for a long time but today I was told that I should check it out.

Quite frankly, I am most disappointed with the tone taken on by some of the members. I am not going to run a forum with these attitudes around and I am sorely tempted to delete this thread and send a couple of guys to the cooler for a week or more.
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  #152  
Old Sun 01 November 2009, 09:15
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
There's been a lot posted on the forum about belt-drives and gearboxes. I searched on the word "chatter" and was directed to "Driving Mechanisms: Rack/pinion, gears, screws, belts & chains". In that section is the thread, "Reduction Drive by belt - a collection of various designs". In the six pages of that thread, you'll find a lot of different designs that have been tried. On page three of the six-page thread, I saw the photos posted by Alan of some mirrors that he cut from oak. I hope that he doesn't mind that I've reposted one of them. That cut was made on his MechMate with motors that had neither belt-drives non gearboxes.

The chatter on a MechMate is very similar to the chatter on a Shopbot when chatter conditions are ideal. That caveat about chatter is important.

On my Shopbot, I didn't always get chatter. On most of the photos posted by MechMate owners, I don't see chatter. But, under the right conditions, especially with non-geared/non-belted motors, many of us get chatter.

On my Shopbot, with 3:1 belt-drive transmissions, MOST of the chatter was eliminated. Sometimes I still got chatter, although the roughness was greatly reduced. Even now, with 7.2:1 Tapered Hob gearboxes, I still get some chatter when the conditions are just right to produce chatter. It could be the gearboxes. It could be the construction of the Shopbot. It could be the lack of maintenance on my machine. It could be almost anything. I've done everything reasonable to eliminate as much chatter as possible, and I just live with what's left and rub it out with a few strokes of sanding. In the case of aluminum, I use a power sander. In the case of plastic, I run over to a nearby glass shop and borrow some time on their wet sander.

Here is Alan's photo:
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  #153  
Old Sun 01 November 2009, 09:44
Alan_c
Just call me: Alan (#11)
 
Cape Town (Western Cape)
South Africa
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Mike,

When I cut those mirrors, it was with two passes at about 4m/min. I have since tried similar cuts at a slower speed and doing rough passes about 1mm away followed by a finishing pass on size. This has given remarkably improved cuts with hardly any chatter. (using spiral / slot drill cutters). I am still going to make reduction drives but it is possible to get very good results if the correct cutting strategy is followed.
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  #154  
Old Sun 01 November 2009, 09:56
chopper
Just call me: chopper
 
Big Lake Minnesota
United States of America
Quote:
Originally Posted by sailfl View Post
Chopper,

Please spell my name correclty
sorry it was a typo
//chopper
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  #155  
Old Sun 01 November 2009, 10:04
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Alan,
Thanks for posting that information. Chatter is often a function of speed and depth of cut. I ran a series of tests on my Shopbot and saw a remarkable difference in chatter depending on how fast the machine was cutting. Recently, I made some cuts in aluminum with the machine running only 50% of the recommend feed speed and only 0.020" per pass. The cuts were very clean and basically chatter free.

There are a lot of factors that have to be watched to get an ideal cut. Many times, when cutting wood, it is much more cost effective to get a quick cut on the machine and then to spend a few more seconds with a sander - especially if I would have to sand anyway.

There was a fellow on the Shopbot forum who sold his original Shopbot because of chatter problems and then bought the newer PRS-Alpha model. He experienced the same chatter problems. He posted a bunch of very blurry pictures that he said showed how bad the problem was. We had to take his word because of the quality of the photos. Because he was using a program that Bruce Clark and I wrote together, I played with his numbers and saw that he had very unrealistic goals. He assumed that since that machine could cut at 12-inches per second, that it should be able to produce perfect parts at that speed. At 5-ips, on my PRT-Alpha, I got almost perfect parts. Shopbot cut some parts at various speeds and also suggested 5-ips as the ideal speed for that material and that type of cutting. He disagreed and returned the machine for a refund.

I've seen some terrible cuts made on a Thermwood when the operator didn't use the right speeds. I've seen some beautiful cuts on my entry-level Shopbot when all the factors were right. The MechMate is a much sturdier machine than my Shopbot. It has less flex and more mass, which would help in those "picky" situations when everything has to be just right for the cut to be perfect.

Although I agree with almost everything that has been posted about the value of adding a belt-drive transmission or a gearbox with zero backlash to a non-geared motor, I don't believe that gear reduction is always the magic bullet that kills all of the common problems that we experience. I've found that gear reduction minimizes the problems to the point that I consider them to be eliminated, but not always.

Your post pointed out the value of a little experimentation to find the best parameters. Thanks.

Last edited by Richards; Sun 01 November 2009 at 10:07..
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  #156  
Old Sun 01 November 2009, 10:17
chopper
Just call me: chopper
 
Big Lake Minnesota
United States of America
Mike,
I couldn't agree with you more, if you are running a reduction to get rid of the chatter and do not use the proper feeds and speeds the reduction will not save you, be it belt or gear.
//chopper
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  #157  
Old Sun 01 November 2009, 11:37
javeria
Just call me: Irfan #33
 
Bangalore
India
chopper - I don't believe that machining Aluminum is the tru test to test for chatter marks,

while cutting Alu - i reduced the step down and the feed rate of the machine - now what happens is that the Alu is beautifully cut, but when i cut ply / mdf at much higher speeds the chatter reappears

today i observed something while cutting 3d too, if I keep my speeds around 3000mm/min the results are great, any higher speeds and I observe pitting,

but I know what the problem is - its me who did not get my Z assy right , I am probably just going to shift to linear rails soon on the Z axis and I dont have any argument over that in my mind,

Sorry Nils I am cluttering your thread with my problem -

and Mike - I agree fully with you- we have to understand the limits and parameters under which to ascertain that we get good cut quality results.

RGDS
Irfan

Last edited by javeria; Sun 01 November 2009 at 11:42..
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  #158  
Old Sun 01 November 2009, 11:58
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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I agree with Alan. As I only havea little 500 W Makita router on my MM, I cannot take deep high speed cuts. This I realised very soon after completing my machine. From there I take it slow and with cuts not more than 1.5 mm at a time. Like Mike said, that sometimes you get a little bit of chatter and other times less. My chatter is so little that with a light sanding they are completely removed....or it adds to the overall 'effect' of the piece I have cut. I actually would like it to CHATTER all the time when cutting flowers, leaves and wildlife scenes.
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  #159  
Old Sun 01 November 2009, 12:14
chopper
Just call me: chopper
 
Big Lake Minnesota
United States of America
Quote:
Originally Posted by javeria View Post
chopper - I don't believe that machining Aluminum is the tru test to test for chatter marks,

while cutting Alu - i reduced the step down and the feed rate of the machine - now what happens is that the Alu is beautifully cut, but when i cut ply / mdf at much higher speeds the chatter reappears

today i observed something while cutting 3d too, if I keep my speeds around 3000mm/min the results are great, any higher speeds and I observe pitting,

but I know what the problem is - its me who did not get my Z assy right , I am probably just going to shift to linear rails soon on the Z axis and I dont have any argument over that in my mind,

Sorry Nils I am cluttering your thread with my problem -

and Mike - I agree fully with you- we have to understand the limits and parameters under which to ascertain that we get good cut quality results.

RGDS
Irfan
I would like to see the cuts you have made in aluminum, yes you can get chatter in any thing you cut I have heard all this before but no one will show their cuts, I would like to compare if you would show them, thanks
//chopper

Last edited by chopper; Sun 01 November 2009 at 12:18..
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  #160  
Old Sun 01 November 2009, 12:24
javeria
Just call me: Irfan #33
 
Bangalore
India
tomorrow sir - its 1 AM here
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  #161  
Old Mon 02 November 2009, 02:35
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
To All,

Any discussion that has to do with chatter is fine with me. I have been working on a couple things that are relate to fixing my problem but have not posted any thing. It makes sense to have the chatter problem in one thread.

I do thing that my racks are not aligned properly and that is what is causing my noise problem that I have had for ever. I don't think it effects that chatter but there has to be binding or there would be no noise. The grantry purrs when the Y car moves.

I did add spacers under my aluminum rails to fix the C Channel not being straight and I think it helped some.

I will post more when I try some things. I recently cut some grills out of .125" 6061 Aluminum and I will be posting results of that. I rarely break bits but I went through 5 in a learning experience and completing the job.

It is interesting to me that some one with a machine like mine, meaning same characteristics.... preground rails and Milwaukee router, can run their machine at 300 IPM and have no chatter and I can not do the same thing - that was cutting my diagonal cut. He has the same motors that I have.

I also don't believe that there is one solution to this problem. I do believe that factors related to my problems have to do with the way the parts of the table, gantry and Z work. I am working on fixing the Z first.

Last edited by sailfl; Mon 02 November 2009 at 02:51..
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  #162  
Old Mon 02 November 2009, 04:13
Robert M
Just call me: Robert
 
Lac-Brome, Qc
Canada
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Nils,
In my amateur to CNC world opinion, I have a tendency to think your problem of chatter / rough cut is a result / consequence of many factors, minute or not on each of them to a point of hard to impossible to locate individually, but combined as a hole, your machine that is ( or others with preground or not rails & a hand router or spindle) get your own result / consequence.
A very important factor, goes to anything build, is attention to small detail while making / producing it !
Not saying you did not take care of details and you where not being matriculate, but what I’m saying is, no one in this forum has the same ability, the same attention to detail, time to make it , acceptance to tolerance and so-on, making each and every ones BEAST a little different vs the next one, even if it comes from the same fabulous, plans!!!.....and that goes with leaving out in the equation, difference in materials to make this beast by it self !

My experience as a hand on making thing for over to many yrs and observering and studying on fabrications methods, and…well….what is going on here as well !!!

My 2cents….No offence to no one was intended and can only HOPE, no one feels offended and NO ONE will attack others for this !!!
AMICALEMENT, Robert
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  #163  
Old Tue 03 November 2009, 07:21
bradyaero
Just call me: Greg #19
 
Smiths Falls, Ontario
Canada
I never run my machine over 200 IPM, as a matter of fact I run it mostly at about 100 IPM. I don't get chatter marks but my rack and pinion are noisier than I would like. When I disengage the pinions, everything is smooth as glass, when I re-engage them the noise returns.
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  #164  
Old Sun 29 November 2009, 06:58
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
My progress and what I have tried:

Since the last time I reported, I have not stopped working on my problem but decided not to report because I was getting too much direction and it was more than I could handle.

1) Spider / Z Tube / Z Plate / Router

This is the first place I put my attention. I felt that I was getting some flex no matter how tight I made the eccentric bushings. I knew that I had not done the best job of drilling the holes for the V Wheel bolts on my spider. The spacing was not the same so I always had a problem aligning and tightening the bolts so that I had tight fit and that all was square.

I decided to replace the spider, Z tube and Z plate. With some assistance from Leo in Tennessee, I had my new parts. Once assembled and I knew things were tight, I installed them. But once again, I could see that there was flex taking place even when I had the eccentrics turned to the max.

I determined that my flexing problem had to do with the fact that I did not used a thick enough washer between the Y Car Bracket and the Spider. When I used a thicker washer, I could back off of my eccentrics and my flexing went away.

I don't think I had to replace my spider and Z assembly but I am happy with the new parts so I am selling my Z assembly.

With this first problem fixed, I tried some test cuts but my cutting problem was not fixed.

2) Belt Drives

There were a number of people that thought that I should have taken up the offer of trying belt drives. So this was the next step.

There is a non documented builder in my area that has assisted me when I tried the computer. He graciously agreed to bring his Chopper built belt drives with motors over to my house so I could test them on my machine.

It took building some interface cables because of the different motor connectors used and changing the position because of different pinion gears but we ran a test. I thought that this solution would resolve the problem.

Unfortinately, the resulting cut with the belt drives on my machine did not cut any better than with out the belt drives. In this case, I do not believe that backlash is the cause of my chatter marks.

If I had to do over again, I would not buy geared motors because of the cost but I would buy direct drive motors and use belt drives but belt drivbes were not being talked about when I started my machine.

3) Mach Configuration

I was begining to believe that my problem was a signal problem so I started to look at my Mach configuration. I did find some things that the Mach configuration manual suggested doing but those changes did not make any difference in the way my machine cut.

One thing I did try at the suggestion of Richards was different Acceleration and Velocity speeds. I determined that a very slow accelration around 10 helped my problem.

4) Rack and Pinion Noise

Since I finished my machine, there is been a noise problem on both X Axis when the gantry was rolling. I thought that sound was an indication that my pinions and racks were not engaging correctly. But how do I go about fixing the problem.

I took some measurements and found that my motor plates were not square to the rails. It wasn't much but it was off. I also discovered that one of my X motor mounts had a slight concave to it. It wasn't much but since I had a spare motor mount, I replaced it.

I removed the noise in my X sides by placing some washers between the Gantry and the motor mount on stationary bolt. When I roll the gantry now, there is a smooth sound coming from my X sides.

My cuts have improved but I would like to see them improve more.

I currently have my X motors tuned to Velocity 450 and Acceleration set at 20.


I hope this information will help others. I will continue to work on getting a better cut out of my machine and I will share my results.

Thanks to all that have helped and those that made suggestions.

Last edited by sailfl; Sun 29 November 2009 at 07:03..
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  #165  
Old Sun 29 November 2009, 17:30
shaper
Just call me: Jed
 
Perth, WA
Australia
Nils

I've been watching hoping to see a good result, it seams you are on your way to the results you are looking for. Great summation particularly given all that has been said and some things there that I'll be watching when I get to the mechanical side of my build.

Thanks
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  #166  
Old Sun 29 November 2009, 23:38
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Jed,

Thanks and I hope you don't go through the process I have been through.
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  #167  
Old Sun 06 December 2009, 02:55
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Nils,

I would be interested to see if this could be something for you to consider.

http://www.geckodrive.com/upload/Step_motor_basics.pdf

Page 10

This talks about cable length (I am sure size and type would also affect this) and the need to add a 470uF cap to the Geckos to create a "Fly Wheel" to smooth out the power feed to the Geckos.

Just another thought as I read more on the Control Systems for the MM.

Mike
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  #168  
Old Sun 06 December 2009, 15:51
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The early model Geckos, i.e. G201, need a 470uF capacitor if they are positioned more than 10 inches from the power supply. The G202 has the capacitor built in. The G203v has been designed to be used without that capacitor. The G25x (which are used with the G540) are also designed to not need that capacitor.

Adding that capacitor will not hurt, but it may not help, depending on the Gecko model that you own.

Nils,
Your systematic approach will eventually lead you to a solution. Keep in mind that if you can reproduce the problem each time you run a certain type of cut, that you can eliminate unpredictable electrical interference from your list. Electrical interference is almost always random.

One thing that you can try is to run some X-axis cuts with the Y-axis firmly clamped in place with heavy-duty clamps. Then run the same type of test with the Y-axis moving and the X-axis firmly clamped. If both sets of tests show high quality cuts, then you can eliminate major mechanical problems as being the main cause of the chatter.

If possible, run a test using the highest voltage power supply that is allowed for your steppers (32 X SQRT(Inductance)). Use the highest value current limiting resistors on your Geckos that are acceptable for use with your motors, i.e., if your motors are rated at 3A, make sure that you use the correct resistor to let the motor draw 3 amps in operation (Amps X 47) / (7 - Amps). Add another filter capacitor to your power supply temporarily to verify that a weak or faulty filter capacitor is not allowing too much ripple to limit the torque of the stepper motors. (My first computer, an Imsai, had a bad capacitor. Every time I added an additional memory board to the machine, it faulted - no matter which memory board I added. The total current draw caused too much ripple for the on-board voltage regulators.) Remember that the large filter capacitor(s) perform a different function than the 470uF caps that Gecko recommends for the G201 driver.

The reason for running a test at full voltage and full amps is to give the machine maximum reduced current holding torque. The extra filter cap is to ensure than the drivers can always draw from a reservoir that has little or no ripple.

Systematically following a list is sometimes the only way to solve this kind of problem. Always start with the most obvious and work towards the least probable.
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  #169  
Old Mon 07 December 2009, 09:37
javeria
Just call me: Irfan #33
 
Bangalore
India
Nils have you looked at the new Z Assy, I have - it has helped me to solve more than 90% of the problems I had in my 3d cuts.
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  #170  
Old Fri 11 December 2009, 02:07
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
I thought I would provide some photos of some cuts I made with my machine fixed.

Cut in oak. The flate surface was cut at 70 IPM and the round over at 50 IPM.

The plywood was cut at 200 IPM.

I am pleased with the way the machine is cutting now.

I have not looked at the new Z.
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File Type: jpg DSCN0555.jpg (169.5 KB, 380 views)
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  #171  
Old Fri 11 December 2009, 03:08
javeria
Just call me: Irfan #33
 
Bangalore
India
so - what fixed it nils?
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  #172  
Old Fri 11 December 2009, 11:37
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
For sure tell. After all of the input we would like to know what fixed it !!!
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  #173  
Old Fri 11 December 2009, 12:05
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Were those cuts on the diagonal?

If those major cuts were parallel to the table axes, then the cutter does make a diagonal (half-way through radius) move when rounding a corner. The marks in this photo shouldn't be present if the motion was smooth?:

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  #174  
Old Fri 11 December 2009, 14:37
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald

I can't tell what you are looking at from the photo you have circled. The cuts are mostly not on a diagonal.

The round over bit was cutting a little too deep and the 1/2" EM I was using was starting to get dull.

Trust me the cuts are smooth.
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  #175  
Old Fri 11 December 2009, 15:47
jeffa
Just call me: Jeff
 
Iowa
United States of America
Nils,

I have tried to keep up with this thread from time to time. Do you feel that you have fixed the problem? If so, would you be willing to share with us what the problem(s) was(were)?

Thanks,

Jeff
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  #176  
Old Fri 11 December 2009, 18:07
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Irfan, Mike, Jeff and every one else,

In Post #164, I tried to explain what I did. Basically, I think it is a combination of things.

1) I do believe there was some flex in the Z / Spider. I used a larger washers between the Y car plate and the Spider. That fixed the flex.

2) For the longest time I have had a noise in my X Axis on both sides. I now believe that my rack and pinions were the cause of that noise.

2.A) I had a problem with my C channel. The legs were not square. I had placed washers under my Aluminum X Rails which helped resolve the squaring of the X Rails.

2.B) There still was noise. I placed washers between the gantry frame 10 20 400 and the X motor swing plates but only on the stationary bolt this allowed me to adjust the pinion gears so that they were in line with the rack. Once I found the right number of washers the noise I was hearing went away. There are a couple spots on one side of the X were there is a slight misalignment but it is less than any thing I was hearing before.

When I did these things, I noticed that my cutting improved on the diagonal and the machine is cutting better over all.

Most likely, I could remove the racks and do a better job of installing them. But the machine is cutting well and the gantry moves smoothly travelling in the X direction. I am not going to mess with what is working.

I hope that helps explain. If you have additional questions, please ask.

Two suggestions. Besure the rack is straight when you install and if you have noise that appears to becoming from the rack area check you alignment.
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  #177  
Old Sun 17 January 2010, 22:12
cab. guy
Just call me: Ron
 
Boise,Id.
United States of America
Hi Nils, sorry to hear about your problem. I made these test cuts recently using aspire,4-1 belt drives,1.5 diametrical pitch pinions and heathenistic large nema 2913 oriental motors.The bit used is a well used 3/8"compression bit @ 2 passes @300" per min.into .75 mdf.Up close there are no discernible ridges.In your samples on the straight cuts shown,there appears to be a cadence of ridges spaced approximately 3/16" apart.
I cant believe run out on router bearings could cause this,I'm guessing your rotational speed at 100 plus cuts per flute per inch.The O.J. Simpson glove does not match up.I also cannot digest the fact that backlash is the culprit,because on a straight run the gears stay in contact with each
other as a result of constant back force of load( cutter against material).
There are some benefits with larger motors using belt drives as pointed out a few months back,no backlash,massive holding power.Good luck on your find. Ron.
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File Type: jpg cnc build 005 (Small).jpg (39.7 KB, 237 views)
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  #178  
Old Mon 18 January 2010, 03:55
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Ron and to any one else that reads this thread

I DO NOT have a problem any more. I am cutting fine. I have fixed my problem and it was NOT by replacing my geared motors with belt drives.

I am using geared motors.
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  #179  
Old Mon 18 January 2010, 03:57
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Ron,

Look at the drawings for what you are cutting and check to see if you have small straight lines for your curves. That can be a big problem when you are cutting some thing. Those little straight lines can screw you up.
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  #180  
Old Mon 18 January 2010, 08:49
cab. guy
Just call me: Ron
 
Boise,Id.
United States of America
Hi Nils, Sorry if I set you off, I was merely in agreement with your suspicions (supportive).
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