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  #1  
Old Fri 21 June 2013, 15:43
theshrub
Just call me: shrub
 
berks
United Kingdom
Accuracy/Precision Guitars

Hi,

I am considering a mechmate build sometime in the near future mainly for guitar building but would also like to be able to cut larger boards so will probably be looking at a cutting area of 1220 x 2440 mm.

My question is what sort of precision can i expect? What amount of error would you see cutting over a metre say?

I have just built a small aluminium kit cnc and it has been a great learning experience but requires constant attention and tweaking to achieve consistency. Is the mechmate prone to these problems? Is anyone else out there using mechmate for guitar work?

Thanks,

Shrub
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  #2  
Old Sat 22 June 2013, 03:20
lonestaral
Just call me: Al #114
 
Isarn
Thailand
Send a message via Skype™ to lonestaral
Hey there Shrub.
Considering a build myself but not as large as yours.

Guitars !
I recently cut a Tele body for someone I know.
I did it on my self built Jgro, which is neither rigid or fast.

The most critical part was the neck pocket.
He was happy with the result.

The accuracy is all down to the build quality.

Sloppy fits and assembly will translate into your machining.
I hope my build will result in a rigid, fast and accurate machine.

The fastest axis I have at the moment is the Y at 850mm/min.
Take your time and do your best.
Good luck with your assignment.
Al
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  #3  
Old Sat 22 June 2013, 04:02
theshrub
Just call me: shrub
 
berks
United Kingdom
Thanks Al,

I built a shapeoko 1mx1m which is lightweight aluminium / belt driven and i'm currently out by 3 or 4 mm per metre which is frustrating. I may be pushing it too hard and just need to accept shallower cuts and slower speed rates for the time being. The mechmate is clearly in a different league.

I'm prepared to put in the time to create a well built machine but when it comes to guitar building i'm a fussy bugger about accuracy and just don't want to invest the time and money on a mechmate build if the precision isn't there.

Good luck with your build,

Shrub
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  #4  
Old Sat 22 June 2013, 05:29
KenC
Just call me: Ken
 
Klang
Malaysia
3~4mm per meter off? Sounded like a poorly calibrated machine which isn't set square to me.
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  #5  
Old Sat 22 June 2013, 05:58
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
MechMate will have the accuracy needed. I think in this case, I would make sure to build 4:1 belt drive setup.
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  #6  
Old Sat 22 June 2013, 07:23
theshrub
Just call me: shrub
 
berks
United Kingdom
Ken - i think it's more to do with the forces applied whilst cutting as the machine is square, taught and calibrated as good as it's going to get. I say 3-4mm per metre but what it actually is is 1-2 mm error over 400mm. That 1-2 mm may not be compounded over a metre so my statement may be innacurate. Either way it's not precise enough for my needs as it is. I need to try backing off on depth and speed and see what happens. What sort of error (if any) are you getting with your mechmate?

Metalhead - Thanks for the recommendation. Any other tips for optimising precision? Is the machine accurate enough to produce repeatable inlay patterns at a finer detail (1-2cm square)?
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  #7  
Old Sat 22 June 2013, 07:54
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Most use rack and pinion drive with no issues. Some use linear guides.

But that is costly and I would try rack and pinion first.

Look at the build threads and you will see the detail folkas are getting out of their machines.
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  #8  
Old Sat 22 June 2013, 09:13
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Accuracy is a "nebulous" thing. When I bought a Shopbot PRT-Alpha, I simply expected that it could cut everything within the stated "accuracy" of 0.0016 inch. I assumed that circles and curves could be cut perfectly and that the only problem I could have would be tool marks if I cut too fast. I was wrong. On curves and circles, the machine "chattered".

To "improve" my Shopbot, I added 3:1 belt-drive transmissions to the X and the Y axes. The chatter was almost completely eliminated.

Using a 4:1 belt-drive transmission as Mike (Metalhead) suggested will be an excellent starting point. Then, if your V-rails and V-rollers are clean and if your machine tracks those rails without creeping up and down on the rails and if your cut speed is slow enough to allow the stepper motors to move the axes without loosing steps and if you use tooling that does not flex when making the cut, you'll have excellent accuracy.

If I were building a CNC machine, I would try to find a way to afford linear rails. They would add about $1,500 to $2,000 to the cost. If linear rails are properly installed, the savings on "wasted" material would quickly cover their cost when extreme accuracy is required.
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  #9  
Old Sat 22 June 2013, 13:48
theshrub
Just call me: shrub
 
berks
United Kingdom
Thanks all for your advice. It sounds like a 4:1 transmission and linear rails are the way to go to further ensure precision. I don't mind spending the extra for accuracy if spending less is going to be a false economy for my purposes.
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  #10  
Old Sat 22 June 2013, 16:08
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
shrub.... these are guitars I cut regularly. Around 50 guitars and necks.
I need something around 20min for all holes and profile. I don't do the round off or arm rest curve.

http://cnc.rs/sr/projekti/muziki-instrumenti.html
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  #11  
Old Sat 22 June 2013, 23:23
theshrub
Just call me: shrub
 
berks
United Kingdom
danilom - Great! did you make any modifications to your mechmate?
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  #12  
Old Sun 23 June 2013, 02:27
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
No modifications, but plan to do some on the Z, for larger endmills and faster removal rate of hardwood I plan to install 3kw spindle. It could improve run time significantly
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