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  #1  
Old Tue 22 January 2008, 14:39
greginwa
Just call me: GT
 
Washington
United States of America
to build or to buy?

I have been looking at buying a shopbot or dynacnc and just came accross the mechmate build idea today. I would like any feedback on the comparitive accuracy and speed of a mechmate build compared to a new shopbot for example.

Thanks,

Greg
  #2  
Old Tue 22 January 2008, 16:00
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Greg,
If you build your own machine, YOU will be responsible for its accuracy and speed. The plans that Gerald has created, if followed, will produce a wonderful machine, as accurate as any on the market that uses comparable parts - which is to say that it will meet the needs of anyone using a CNC router for wood-working. You can use any motors and any motor drivers that you want, so the speed will be as high or low as your budget allows.

A new PRS-standard Shopbot will cost about 2X as much as a comparable MechMate. The PRS-Alpha Shopbot will cost much more than the Mechmate, but it also uses motors that are higher performance than the motors that most MechMate builders are going to use.

I own a PRT-Alpha Shopbot. It is a good machine, but it has a lot of limitations, most of which Gerald has fixed in his design. If I had room in my shop, (and if I knew anything about mechanics), I would build a MechMate. I have no room and I can hardly turn a screw much less weld two pieces of metal together, so I'll use what I have until it breaks and then I'll re-visit the build vs buy argument.
  #3  
Old Tue 22 January 2008, 18:45
paco
Just call me: Paco
 
Québec
Canada
Oh! That is actually interesting!

I'm considering upgrading my tool size and I face different avenues. I could sell what I have right now (PRT Alpha 48X96) and buy a complete new tool of the size I need (PRS Alpha 60X120), buy a PRS 60X120 hardware upgrade or build a MechMate and fit it with my motors and electronic setup which I'm happy with. My main (and currently only) concern about building a MechMate is if my current motors (ASM98AA-T7.2 and ASM911AA for the Z) will fit. The Xs and Y have large pinions and the Z a smaller one... will the motor mounting holes will match?... Can the wheels (V-rollers) can be off-the-shelf ones or will I really need to have the wheels machined to fit on bearings? I know that are pretty simple problem but I decide to post to have some thoughts and opinions about my project. I have followed some of the discussions over the time since the start and I've downloaded the documents to browse 'em rapidly only yet.

I'm very confident about the MechMate design and I feel pretty sure about about my capability to build it as I regularly do some metal works and mechanic around.

I hope I'm not hijacking Greg's thread too much; I was to start another one but I thought why divide the information as this may help Greg too...!?

Thanks in advance.
  #4  
Old Tue 22 January 2008, 21:08
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Welcome Greg,

Quote:
Originally Posted by greginwa View Post
. . . any feedback on the comparitive accuracy and speed of a mechmate build compared to a new shopbot for example.
The differences in speed and accuracy are not significant enough to base your build/buy decision purely on that. The biggest question is whether you have the skills, tools, time & patience.

Quote:
Originally Posted by Richards View Post
The PRS-Alpha Shopbot will cost much more than the Mechmate, but it also uses motors that are higher performance than the motors that most MechMate builders are going to use..
It is debatable whether those high performance Alpha motors produce a CNC machine which is better than one with "standard" motors.

Quote:
Originally Posted by Richards View Post
I own a PRT-Alpha Shopbot. It is a good machine, but it has a lot of limitations, most of which Gerald has fixed in his design.
Mike's ShopBot is not being produced any longer. ShopBot have totally redesigned their machine to make extensive use of aluminium. Owners are finding this to be a flexible machine and are adding extra legs to cure the sag in the table.

Quote:
Originally Posted by paco View Post
. . if my current motors (ASM98AA-T7.2 and ASM911AA for the Z) will fit. The Xs and Y have large pinions and the Z a smaller one... will the motor mounting holes will match?... Can the wheels (V-rollers) can be off-the-shelf ones or will I really need to have the wheels machined to fit on bearings?
The motors will fit to the mounting plates. What are your pinion sizes? All pinion sizes can be accommodated with a bit of extra planning. The wheels are off-the shelf from at least 2 companies in the USA - no machining needed.
  #5  
Old Tue 22 January 2008, 22:47
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
This is probably the wrong area on the forum to discuss stepper motors but there are some differences between the PK motors that most MechMate builders are going to use and the AS (Alpha) motors. First, the Alpha motor has built-in feedback. That feature, as implimented on a Shopbot is totally worthless. It is not a closed-loop synchronized system that some would want you to believe. Granted, most of the time the motor does not stall, but the cut is ruined anyway. The more important difference is that the Alpha motor and the Alpha AC driver produces 400 oz*in of torque at 1000 RPM. The only PK motor that even comes close to that performance is the PK299-F4.5 motor when it is wired parallel. That is the only real difference between the PK motors and the Alpha motors except for cost. ONE Alpha motor costs about the same as FOUR PK motors and FOUR Gecko G203v stepper drivers. The other difference is that the PK motors give you 2,000 steps per shaft rotation and the Alpha motor gives you 1,000 steps per shaft rotation - so the PK motor has 2X better resolution. The lower resolution combined with the higher torque allow the Alpha motors to give a useful feed speed of 8 to 10 inches-per-second (if you have a huge spindle, a huge vacuum hold down, and expensive spiral cutters).

I don't advocate buying the Alpha motors. If my machine didn't come with them, I certainly would not have ordered them as an option.

As Gerald pointed out, the new model Shopbot is made out of aluminum extrusions. I have a good friend who owns the newer model machine. He lives just four miles away, so we visit each other's shops frequently. His machine cuts better than mine - much, much better; but, there is still ample evidence of flexing and still some chatter. In other words, neither the $8,000 PRS-Standard nor the $15,000 PRS-Alpha machine is as well built as the MechMate. Under the right conditions, the $15,000 PRS-Alpha might give you 2 or 3-inches per second faster cutting - but at about 4X the price.
  #6  
Old Tue 22 January 2008, 22:48
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Welcome Greg.......How many Gregs are we up to now?
  #7  
Old Tue 22 January 2008, 22:57
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
About 30 Gregs registered, about 6 have posted.

The biggest difference between MechMate and the ShopBots, EZ, Sabre, Techo, whatever is the weight/mass. The commercial producers have to build light to be competitive for production processes and for shipping & handling. They also have issues with limited time to setup & calibrate (and then dismantle to ship). If they use their own in-house control software, they don't have the time to test it under all conditions (inches/millimeters, XP/Vista, Serial/Parallel/USB, 115V/230V, etc.) They are under huge commercial pressure to produce something faster and glossier than their peers. They have to buy into the myth that shiny aluminium is the best way to go, supporting the other myth that lower weight is better. (The +$100k machines are all heavy iron for good reasons - Thermwood, etc)
  #8  
Old Wed 23 January 2008, 00:23
greginwa
Just call me: GT
 
Washington
United States of America
Thanks for all the great feedback. At this point I'm leaning heavily toward building a Mechmate. The cost difference is very attractive of course, and I think it would be a great learning experience. I have 25 years as a multiaxis cnc programmer, so I know cnc and metal parts machining. I've had some experience with 5 axis Thermwood routers (including having the tedious job of calibrating the 5 axis head), so I feel confident I can put one of these together with all the help that is available in this forum.

Thanks to Gerald for creating this Mechmate community. I hope that by building a machine of my own I can contribute to your cause.

Greg
  #9  
Old Wed 23 January 2008, 06:39
Robert M
Just call me: Robert
 
Lac-Brome, Qc
Canada
Send a message via Yahoo to Robert M Send a message via Skype™ to Robert M
Greg,

I’d like to point out some other reasons for you to consider MM
From all the other CNC brands (that I know/seen and I’ve been wondering around from nearly 2ys in the back ground if this group and over 4ys looking at what others have to offer) you may just find a better machine. True, if ever you put some value to your time spent in the making of this Blue Beast, you may come close to a total estimated value to some machines out there, but one important thing nobody has mention yet… no where else they will offer you the adventure of being part of a self builder and part of the MM community/family. No where else !
It may be strange coming out from a guy like me to say those things since I have not yet built one, but that does not stop me from witnessing these and other facts. And last but not the as important as above, you’ll become the best and most reliable tech / repair guy for your machine you’ll ever encounter !!
Many advantages can be said, no where else you will find what here
Amicalement, Robert.
  #10  
Old Wed 23 January 2008, 07:57
GregA
Just call me: Greg
 
Dundee MI
United States of America
Well, here in the midwest, it would cost about $3000 dollars to have a fabrication shop do ~all~ the welding (but not laser cutting) , paint and deliver the device. From there I leave it as an exercise to the reader to figure in, the comparative price to a shopbot, because it will matter depending on what parts you choose.
  #11  
Old Wed 23 January 2008, 08:12
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Greg (can't have enough Greg's as far as I'm concerned)

I can't say enough of the support given freely here. I am totally new to CNC of any sort. I have never operated or programed one before. Think about that for a second .... now I'm building one. That's incredible!!

The only reason this is possible is because of the help from Gerald and people all over the world. I have gotten better, faster (within hours), and more accurate information from this site, than from local merchants.

My decision to build a MechMate was based on the solid construction, free plans, and the information flow of this site.

My recommendation: BUILD A MECHMATE. I'm not saying it will be easy, but you will have a blast.
  #12  
Old Wed 23 January 2008, 09:22
GregA
Just call me: Greg
 
Dundee MI
United States of America
Quote:
Originally Posted by Greg J View Post
I'm not saying it will be easy,
Nothing easy is worth doing...
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