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  #1  
Old Sun 02 December 2007, 14:29
plain ol Bill
Just call me: Bill
 
Olympia, WA
United States of America
DXF files - where are they?

Gerald where (or is there any) .dxf version of the drawing available? I notice on the .pdf version that we need to submit .dxf to laser vendors. Any help appreciated and thanks for all your efforts.
  #2  
Old Fri 07 December 2007, 20:32
plain ol Bill
Just call me: Bill
 
Olympia, WA
United States of America
DXF measurement format

Hi Gerald - I know you will spot this and enlighten me. Being out of whack with the rest of the world on measuring things I thought I better ask before I confuse myself even furher (and it's not hard for me to do either). This old head of mine has never worked in the metric system so when I go to convert drawing measurements to something I can wrap my old mind around I think they are shown in MM on the .dxf files? I can convert to our feet-inches if so. Thanks --
  #3  
Old Fri 07 December 2007, 22:00
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
You can scale the whole mm drawing by a factor of 0.039370 to get it in inches.
  #4  
Old Mon 10 December 2007, 22:11
BHawthorne
Just call me: Brad
 
Wichita, KS
United States of America
When I import DXF files the CAD/CAM apps usually just ask me if I wish to use the file's units. I always just select yes and then convert to inches in my app preferences. This works good for me in Catia and FeatureCAM so far. No idea in other apps though.

Last edited by BHawthorne; Mon 10 December 2007 at 22:25..
  #5  
Old Wed 02 January 2008, 10:33
McMark
Just call me: Mark
 
Monongahela, PA
United States of America
It looks like that if you want to import the geometry into something to generate code (such as MasterCam), you will have to scale it to .03937 no matter what units that you are using (Maybe just the USA guys). At least the couple of dxf's that I checked. Kind of like it was drawn using metric dimensions under inch AutoCad parameters. You may want to let your Laser Cut guy know this or you may have the Guinness Book of World Records MechMate on your hands. BTW, I'm hoping to start my MechMate in Jan 08
  #6  
Old Wed 02 January 2008, 16:55
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Mark

I ,also, noticed that when you import the DXF files into MasterCam there is a discrepancy with the measurements. For example in drawing 10 20 456 PA the 147mm measurement is actually 147.5mm when measured using MasterCam. The 128mm measurement is 127.694mm.

In one of the drawings, Gerald does say that the measurements on the DXF files are for reference only.

At first, I thought it was because I had MasterCam configured in Imperial measurements and when it was converted to metric (by multiplying by .03937) it lost a little to rounding off. However when I reconfigured MAsterCam to start with metric there was still a discrepancy when importing the DXF file.

Is accuracy that important for the laser cut parts? I don't know. I am waiting for Gerald to come back from vacation to ask him.

Paul
  #7  
Old Wed 02 January 2008, 18:56
McMark
Just call me: Mark
 
Monongahela, PA
United States of America
I see that the dxf dims are for reference, but the dxf's are there to give to the cutting guys as actual geometry. That being said, and with the dxf's in there current state, the 127.694mm part would come out as 127.694 inches if cut to the geometry. Anyway, I was just trying to save some headaches by pointing out that the scale needs to be corrected or at least checked before sending the dxf out to your cutting guy. If using the geometry to cut the parts, then the actual size will be built into the part so to speak, 127.694mm irregardless of the visible dimension assigned.

Mark
  #8  
Old Wed 02 January 2008, 21:44
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
You're correct, Mark, when you say that the 127.694 mm measurement will be exactly that after being laser cut. That would mean that the part would be .306 mm smaller than what was intended. That fraction of a millimeter is pretty small. I wonder if it would matter if the part was that much smaller? If not that drawing, being accurate may be critical in other drawings.

I may be missing something (tolerances, settings) when importing into MasterCam. I don't have autocad on my computer at home. It would be interesting to see if the sizes are accurate when read by autocad. There must be others that have measured the accuracy of the drawings using autocad. Anyone?

I am going to experiment a little with the DXF drawings to see if the error is in Mastercam or the drawings.

Paul
  #9  
Old Thu 03 January 2008, 03:23
McMark
Just call me: Mark
 
Monongahela, PA
United States of America
The geometry is the correct size, the dimension rounds up. All depends how you have the parameters set in AutoCad. I would trust the geometry provided that you check the scaling, not the visible dimension.

Mark
  #10  
Old Thu 03 January 2008, 05:27
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Gentlemen,
Don't forget that the dimension precision also will "show" a different size depending on what the native drawing was set to before it was dimensioned. For example....the part maybe drawn at exactly 12.5mm, (which is .492125.. inches) but when dimensioned it might read 0-1/2" due to precision rounding. It's an AutoCad thing I deal with daily when working between SI and imperial units. I personally don't loose sleep over it. I have welded up all my parts and all my components seem to work fine.
Sean
  #11  
Old Sun 06 January 2008, 12:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
"Accuracy" is not as important as some of you may be thinking . . . .

The spring loaded motors take up "inaccuracies".....

Lots of slotted/oversized holes.....

Much mention of shimming.....

Don't read too much into the fine decimals that your CAD or CAM drawings are giving you from the .dxf's. The design is intended to be very tolerant of discrepancies between the metric and inch systems. Without spending hours checking everything again, I am still 99.999% confident that your laser cuttings won't end up as scrap.
  #12  
Old Sun 06 January 2008, 12:42
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Thanks, Gerald. I am taking the files and printed out drawings to 3 places tomorrow (Monday, Jan 7) for quotes. I have opted for the geared motors, so I will be using the "optional" DXF drawings. Including the skate drawings, I have 19 files to make 24 pieces. I will post the results.

Paul
  #13  
Old Wed 09 January 2008, 17:59
kanankeban
Just call me: Hector #89
 
Monterrey
Mexico
Hello everybody,
Thanks Gerald for such a good work and specially for sharing it!
Planning to start building soon, maybe first Mechmate in Mexico...Do you know someone that has done the cutting using High Definition Plasma (Not normal plasma). It turns out that I can get the cuts for free on a High Definition Plasma, they told me IŽll get about +/-0.006" of tolerance in the cuts. As you mention that the design is intended to be very tolerant of discrepancies my dopubt is if +/-0.006" might be right for fabricating the parts?
Kindest Regards,
Hector Quintanilla
  #14  
Old Wed 09 January 2008, 22:24
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Hector, ask them for a sample first, or visit their shop. Look at how neatly they can cut the small holes and judge it from there.

Cutting the outlines should definitely be okay, you might rather want to drill the holes.

0.006" is more than accurate enough - if it was true. I havn't seen a plasma, or even a laser for that matter, which cuts that accurately. There are also some tiny glitches and excuses why they don't get to the figure they advertise.

On the "accuracy" of the steel cutting, I could use a bandsaw, jigsaw, drillpress, files and time to build a MM that will cut better that many MM's produced with precision laser cuttings. The MM's precision comes from the attention to the assembly, the shimming and lining up of the rails and rollers.

For the steel cutting, the laser process is suggested because it is fast and relatively cheap for the time it saves. Also, it is always done with clean steel, free of rust. The accuracy is a bonus.

15 years ago, before laser arrived here, we were printing drawings full-size, gluing the drawings to steel sheets, center-punching, drilling, sawing, filing, grinding, etc. and we were building good machinery.
  #15  
Old Thu 10 January 2008, 04:38
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Interestingly enough, I still print parts full size and spray glue it on to the parts. Its quick, accurate and leaves little mistakes for the "guys in the shop" with a tape measure.

Sean
  #16  
Old Wed 06 February 2008, 10:56
ekdenton
Just call me: Ed #8
 
Alamogordo, NM
United States of America
quick question on .dxf format

Newbie at this and I am not up yet on all the computer stuff. How do I convert the plan photos to a .dxf format, in order to send part layouts to get lazer cutts?
  #17  
Old Wed 06 February 2008, 11:09
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Ed,

On the very first page of this web site is the download thread.

Click on download and at the bottom are some ZIP files. The directions are there also.

Hey, finally someone close to me. Welcome.
  #18  
Old Wed 06 February 2008, 11:30
ekdenton
Just call me: Ed #8
 
Alamogordo, NM
United States of America
Thanks Greg, I found them.
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