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  #1  
Old Sun 22 January 2006, 04:14
Gerald_D
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The original MechMate - Cape Town, South Africa

These videos edited into first post of thread on 28/09/07:

The big MechMate built from scratch: (Front of dust foot removed)
http://www.youtube.com/watch?v=hGVQQf_iQpI&fmt=18

What was originally the 8x4' Shopbot is now fully converted except for the X-rails, x-racks and x-pinions:
http://www.youtube.com/watch?v=uGQ2J4GgXkg

The workshop where it started - now the home of CAM Craft
http://www.youtube.com/watch?v=dSelxyC5LU0
This thread originally started here:
The beast shown below is what we have named the MechMate. We had to find another name because it is not a ShopBot, although many parts are interchangeable. The pics today are after a strip down and during the paint and re-assemble process. Motors and cables must be re-installed (the z-motor is only balancing there):














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  #2  
Old Wed 24 May 2006, 07:45
Gerald_D
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Some long overdue pics:




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  #3  
Old Thu 25 May 2006, 05:38
Paul A
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Hi Gerald

A very neat and tidy Job, it looks nice and rigid.

What is the grey and white box with the banana sockets ?..... do you have any idea of the gantry weight.

Regards


Paul
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  #4  
Old Thu 25 May 2006, 06:23
Gerald_D
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The banana sockets go to the "Inputs" of the control board (one ground/earth). That is where the z-zero plate gets plugged in now, but it could be anything in the future. Thought it would save laying cables and allows spur of the moment experimentation.

I must remember to weigh the gantry when the motors are dropped. You might have realised (when we met) that I am not that weight-conscious....

Tidying up the electrical box is the main thing now.......
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  #5  
Old Fri 26 May 2006, 07:02
Gerald_D
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The gantry weight/mass, with motors, y-car, hose, cables etc (fully loaded) is 85kg (187lbs).
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  #6  
Old Mon 29 May 2006, 22:48
mikejohn
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Gerald
Looking at the spoilboard, this machine appears to have done a fair bit of work.
Are you in a position to make a direct comparison with the original machine?
In particular, your opinion of quality of cut with the more rigid construction, and different drivers/software.
Can you also give an opinion on spindle against router?
I do like the features you have added, in particular the position of the emergency stop botton, the use of a 'brush' type dust foot, and the banana sockets.
Do you have cable chain on the x axis?
Are the x-rails beefier than the PRT, to allow for the reverse position?
It looks good, very good.

...........Mike (forgotten my password )
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  #7  
Old Tue 30 May 2006, 00:32
Gerald_D
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(I can't see everyone's passwords, so you have to restore your own via this link or tell me to give you a temporary new password)

Hi Mike.

Yes, the "MechMate" has been busy, and that spoilboard has had a couple of re-surfacings - I just took the photos on a bad day. (The spoilboard started off as thick as the base board)

A direct comparison to the standard PRT is a bit tricky because the changes have been gradual:
- the standard PRT first got a MechMate gantry and y-car, but the control software/driver was retained, then
- a whole new machine was built with gantry, Mach, & Gecko.
And there are other small things in between too.

But the bottom line is that there was never a WOW moment, when it looked like a major improvement was achieved.

The biggest difference came from changing the 4-piece y-car to the 1-piece y-car with an idler roller under the rail to simulate the hold-down of the y-motor on the opposite side.

Right now we have practically two identical table and gantry systems (except that one gantry is 600mm longer and carries a much heavier spindle/dustfoot). Both have identical direct drive motors and the pinion diameters are very similar. The controls are as follows:
- Short gantry, light load has ShopBot control board with IMS drivers, under DOS software
- Long gantry, heavy load has Gecko drivers under Mach3 software.
The quality of cut and speed is marginally better (10-20%?) on the big machine.

I could make a much higher speed on the Gecko machine because Gecko's can easily be told to "over-drive" the motor currents. My impression is that some of the guys with fast Gecko routers are actually over-driving the motors. (Our Geckos are set to the limits stated by the motor manufacturer)

The spindle is much quieter than the router. So far there is no other big advantage in the type of work that we are doing.

X-axis does not have cable chain...yet. So far we are having good life out of a flexible tube that holds the cables together, even on our earlier machine.

The rails don't have to be any beefier to allow them to be reversed - in fact they could technically be lighter because they are more "under" the load point of the roller. The "reversed" rail makes the table a lot more spacious. Also, during the setup and alignment of the angle-iron rails on top of them, it is a breeze to use small g-clamps to hold the rails together.
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  #8  
Old Tue 30 May 2006, 01:34
Mike John
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Thanks for the password info.
Without wanting to create further disharmony in the CNC community, I must ask why you feel others are claiming much better improvement when only replacing the driver/software side of things? (although I do note that there are no longer exagerated claims about great improvement on cutting times).

........Mike
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  #9  
Old Tue 30 May 2006, 02:40
Gerald_D
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Mike,

For a short period (summer 2000?), ShopBot used some very good IMS drivers, and we happen to have one of those machines. So, our experience of the ShopBot drivers is not typical.

Which brings me to the point that there probably isn't a typical (or bench-marked) ShopBot against which claims of improvement can be made. Many different motor sizes, gearbox ratios, pinion sizes, driver types, software versions by ShopBot on the one side, and quality of owner-supplied PC as well as setup on the other side.

Our Gecko experience is also very limited, and we havn't tried to push them, or the motors, to their "smoke" limits. We are plodding along by the conservative book.

Basically, my opinion should count very little in this because a back-to-back comparison between 2 machines should be simple enough to arrange.
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  #10  
Old Sat 17 June 2006, 10:08
Mike John
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Gerald
Didn't know where to ask this question, so I put it here!
Did you ever decide on a simple 'keyboard' with minimum keys for Van to operate?

...........Mike
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  #11  
Old Sat 17 June 2006, 11:13
Gerald_D
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The "Van" that we have now can move the mouse cursor and click on the right buttons on the Mach screen. (A touch-screen would make it even easier). He is happier with the Mach screen compared to the SB DOS screen.

However, that "banana box" and the E-stop boxes are soon to be replaced with the dumb-Van version...
- The E-Stop boxes will get two more buttons each: Resume & Pause.
- The banana box will loose 2 bananas and gain 3 buttons. Then the four buttons will be E-Stop, Resume, Pause,& Z-Zero (black). The two bananas are for the plate "switch".
With that huge table, Van sometimes crawls over to the spindle to do something there, and buttons only at the ends of the gantry are out of reach. The pause/resumes at the ends of the gantry are for moving clamps during a job.

There is a huge difference between E-Stop and Pause. The "E-Stop" on a standard ShopBot is just a gentle request to the control board to please stop movement, and one can happily "resume" after an SB's "E-Stop". In effect, the SB only "pauses".

A true E-stop cuts power to the router/spindle as well as to the stepper motors, on top of the gentle request to the controller. You can be sure that the system loses its sense of position during this crash-stop, and a simple resume will not get you going again. But you have a better chance of having all your fingers after a true E-stop.
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  #12  
Old Sun 02 July 2006, 14:00
Gerald_D
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At last, the MechMate is complete (99.5%):




That guy is Rapi, been around for only 3 days, and can repeat the same cut file over and over without touching the keyboard.
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  #13  
Old Sun 02 July 2006, 16:46
David Rosenbleeth
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Gerald: Had to register (finally) just to tell you how good it looks. A most excellent and elegant job. I look forward to my "Mech-anized" PRT96.

Dave
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  #14  
Old Sun 02 July 2006, 18:25
Patrick Toomey
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Gerald, That thing looks awesome. The level of workmanship and attention to detail make it look like a high-end commercial machine. Most DIY CNC machines look, shall we say, "home brew". Great work!
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  #15  
Old Mon 10 July 2006, 01:36
Alan Conolly
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Gerald, Thank you once again for the personal tour over your machine last week, a truly impressive piece of engineering especially the finishing and attention to detail (sealing of unwelded joints areas etc.) The wiring in the panel would also embarrass many a "professional" machine builder. a great inspiration.
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  #16  
Old Wed 26 July 2006, 13:55
Wayne Painter
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G'day Gerald,
I must say, an awsome looking machine.

I too have added cable chain to the Y-axis almost identical to how you have done. As well, I added cable chain to the X-axis as I did not like the cables dragging back and forth on the concrete floor. This also allows the "bow" on the SB to only be used for the dust collector which has the added plus that it is away from the other cables. I really like the way the cable chains work.

Very nice JOB!

wayneo
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  #17  
Old Fri 08 September 2006, 06:37
Peter A
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Hi,

I have made my own CNC plasma table and I have just gone out the other day and put in a cheap router. It is awesome to watch it cut with the router. I don't know now if it is better to watch plasma cutting or router cutting.
Anyway. I too have use the vee bearings and my machine is a similar size to yours. I had trouble with gantry flex and wobble when driving it from only the one side. So I had to put a motor on the otherside with a rack etc.

When your table is on and the motors are energized. If you put your hand on the gantry end that does not have the motor, can you move it??

Also, because I have never cut wood with a cnc before. How do I hold the wood down? I can't afford a vac. table. I have heard that double sided sticky tape works good?? is this true?
And do you leave "holding tabs" in a part that you cut so that it will hold together in the wood and not fall out etc etc.

Cheers
Apples
Australia
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  #18  
Old Fri 08 September 2006, 06:49
Gerald_D
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Hi Peter

There are motors on both ends of the gantry.

You can find a lot of information on CNC wood routing by looking at http://www.talkshopbot.com/forum/messages/29/29.html
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  #19  
Old Sat 07 October 2006, 04:00
Mike John
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The following 5 posts were first posted here. Since they are of a wider topic than just the Control Box, they were moved to this topic.

It seems to me that any true evaluation and comparisons between the 4 possibilities will not happen on the Shopbot Forum.
Brady has always posted from biased point of view on anything and evrything, from spindle/routers to that awful Part Wizard.
So can we honestly evaluate the current position here.
I had my table made for me locally, as have many (most?) others.
So Tables do not come into the evaluation.
My PRT control box is now considered sub-standard even by ShopBot themselves.
The stepper motors are third party.
There are many add ons and alterations to the basic shopbot, including means of strengthening carriages to take out slop.
G-code is the industry standard for CNC operation.
So, if I dont use a Shopbot table,control box,software, and I am changing the original Shopbot parts, would it be wise to re-invest in another Shopbot?
Is there a comparison between the cost of upgrading the control box/software?
How difficult will it be to get a proficient engineering company to make the mechmate bits from the drawings here?
I have got this far because I bought a Shopbot.
It seems to me I can progress by tying myself to whatever advancements Shopbot decide to introduce, or follow the ideas muted on this forum.
Mike said elsewhere it isn't a question of what Shopbot was in the past, or is today, it's where will they be in the future?
A lot of recent posts have been very technical.
From all the ideas being thrown around, is anyone willing to describe the 'best' CNC machine we could have, today, for reasonable money?

...........Mike
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  #20  
Old Sat 07 October 2006, 05:48
Gerald_D
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So, if I dont use a Shopbot table,control box,software, and I am changing the original Shopbot parts, would it be wise to re-invest in another Shopbot?

Mike, if you were living in America, where Durham is a quick toll-free call away, and replacement parts will get to you overnight, and want to sing ShopBotYeah My Lord around the camp while holding hands, then ShopBot is the best social option. Somebody will help you with any woes, or take pains to convince you that you are actually doing better than the guys who bought something else. In your case, I don't see any need to invest in another ShopBot. But, if you have been happy with the first one, why not get the same again?

"How difficult will it be to get a proficient engineering company to make the mechmate bits from the drawings here?"

I am doing the drawings to the same standard that I use in my "day-job" company, and those drawings are used fairly painlessly in Brazil, Singapore, Czech Rep., UK and Germany. The drawings here are far from complete, and I am not going to be pressurised for a completion date. The big reasons for the slow drawings are that I don't want the plans to be limited to one size of table only, and I underestimated the number of folk who insist they cannot work in millimeters. (I am also dumbfounded by those who want this huge beast of a machine for serious CNC work, but have no idea what a .dxf drawing is...)
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  #21  
Old Sat 07 October 2006, 13:52
Gerald_D
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Mike_in_Romania, May I suggest you take a similar route to me....

I first built just a gantry and y-car to get some confidences. Fitted them to the PRT table and rails and swopped over the wires and motors. And that machine is still running in that state more than a year later. Once the confidence was gained there, the MechMate was built from the ground up.

(....which means that I have a surplus PRT gantry and y-car lying somewhere. I actually want to have another look at it now that the "AGension" clan are asking for ways to beef up their moving parts.....)
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  #22  
Old Sun 08 October 2006, 09:40
Mike John
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Gerald et al
There is a thread onthe Shopbot Forum mainly from the 'other Mike', that seems to suggest an inexpensive upgrade to better than Alpha, a lot less than via Shopbot, and apparently a lot better and safer.
My PRT has the Alpha construction (its a late one).
Is this the way to go before moving on to a second machine (which may be needed late Spring 2007)?

Incidentally, I can't imagine a lot of those postings are going to stay!

.......Mike
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  #23  
Old Sun 08 October 2006, 09:53
Gerald_D
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Mike, do you have an English-speaking engineering shop nearby who I could communicate directly with? They might be interested in doing a small run of gantries for you to sell in your neck of the woods - it seems as if they produce good quality at low prices. Food for thought.......

When I mentioned the confidence building in the earlier post, I forgot to mention that I also built a very rough Mach/Gecko "control box" which was temporarily plugged into the ShopBot. That also worked. So, after testing my DIY gantry, y-car and control box, and after already having built one table, the only grey area was the z-slide - all that was left to do was to go shopping for more motors and other bits of standard hardware.
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  #24  
Old Sun 08 October 2006, 11:45
Mike John
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Gerald
English speaking no, but I have a good interpreter
My router mount, which I may have mentioned, cost $20 including VAT.
My table cost, less steel, 400.

I have chatted with them about the Mechmate idea
They say the first one will cost as much as the next 10!!
Which is always the way.
Don't forget, in 85 days our 'internal' market will be over 485 million, dwarfing the USA's 292 million.
We could be on to something !!!!

.........Mike
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  #25  
Old Sun 08 October 2006, 12:16
Gerald_D
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"the first one will cost as much as the next 10"

...which means the router mounts come down to $2 and the tables down to $40....we could live with that!
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  #26  
Old Sun 08 October 2006, 18:01
Mike Richards
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Mike J,
As far as I'm concerned, the Alpha motors add nothing to the Shopbot. A PK299-02, PK299-03, or PK299-F4.5 all have the same speed and torque characteristics if driven by Gecko G202 driver and a power supply with about 20X their rated voltage. In fact, the PK steppers w/G202 drivers would have 2X or 4X the resolution of the Alpha motors, since the Alpha motors can be set to either 500 steps per revolution or 1,000 steps per revolution. The other factor is cost. You could basically buy four PK motors, four G202 drivers and rig up a good power supply for the cost of ONE Alpha motor/driver.

I think someone at Shopbot got completely snowed by the feedback feature of the Alpha motors, didn't understand how to implement it, and now is too proud to admit that "lesser" motors would actually work better.

On my machine, the Alpha motors finally work after being geared down 3:1. I'm sure that if I installed PK299-02AA motors, I'd have to gear them down 3:1 also - since they are so similar in every respect, except feedback, to the Alpha motors.

Those of you who are lucky enough to already have geared 1-amp motors only have to decide whether you prefer the Agek/Shopbot or the Ascension/G-code better. Either way, you'll end up with about 5X the resolution and probably 2X the speed (maybe more) based on the fact that the original Shopbot controller card sent out 400 pulses per motor shaft rotation and a Gecko G202 puts out 2,000 pulses per motor shaft rotation. If you ever need a lot more torque and more speed, you can swap out the motors, build or buy a gearbox for each motor, build or buy a bigger power supply and you'd have a machine functionally equal to the Alpha.
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  #27  
Old Mon 09 October 2006, 00:22
Mike John
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'Other' Mike
Are you suggesting that the much trumpeted feedback of the Alpha motor is an over rated benefit?
It does seem that is the one thing missing from an 'improved' PRT. As I said before, my carriages etc. are as on the Alpha, so that is not 'missing'.

..........Mike
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  #28  
Old Mon 09 October 2006, 00:39
Mike Richards
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Mike J.
The Alpha motor's feedback absolutly does not work - in my opinion. Granted, if something causes the motor to slow down, it can recover and regain its position without losing steps. However, think what happens. If one X-axis motor slows down and the other X-axis motor does not, the cut is 'bent out of shape'. When cutting a circle, if any one of the three motors involved slows down, you end up with an elipse, not a circle. There is NO coordination between the motors. To work properly, if one motor slowed down, all motors should slow down - or the cut will be ruined.

With 3X the torque because of the belt-drive gearboxes on my Alpha, I no longer have any problem with any of the motors slowing down. (I've got 1,800 oz*in of available torque.) The 1-amp 3.6:1 stock motors on the PRT have about 300 oz*in of available torque, which is the main reason that I'm beating the drum for larger PK299-02AA motors with gearboxes as a 'required' upgrade for the PRT machines.

If a PRT machine's stepper is overloaded, it misses steps and the cut is ruined. If an Alpha machine's stepper is overloaded, it slows down and swerves, and the cut is ruined. The net effect in ether case is that the cut is ruined. Why pay $1,200 for an Alpha motor when you can do the same damage with a $200 PK299 motor.
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  #29  
Old Mon 09 October 2006, 01:20
Gerald_D
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Mike_R
I am not going to join you on beating the drum for over 1000 oz*in of torque fed into the typical table/rack/pinion we sit with today. What do you want to do with so much torque? Accelerate the gantry faster? (Is it stiff enough). Apply higher cutting loads? (will the spindle/holddowns/racks/pinions/gantry_deflection handle it?). Reach higher jogging speeds? (Is the system safe enough if it should hit an arm or a stop?) Etc.

You happen to have a very high torque now that you've fixed the gearing, but is it usable/desirable as a target by itself?
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  #30  
Old Mon 09 October 2006, 01:28
Gerald_D
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Mike_J
What you have sitting on your floor in terms of table/rails/motors/gantries/gearboxes/etc. are all okay. But the control box on your desk could be seriously improved - as demonstrated by Ascension, Agek and now SB themselves.
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