New machine assembly...any suggestions?

[rickwoody]

Hello all,
I just purchased a PRT that was still in the original boxes and never assembled:D. It was listed on this forum and hopefully it will be a good deal for me and do what I need it to do. A few of y'all provided some input on my purchase and I really appreciate that. Thanks Gary, Mike, & Monty! I went with Shopbot to use the eCab link and I'm really impressed with the participation of this forum.
The machine I bought is a '04 PRT96. It has 2 Z's and an indexer. The steppers are the 3.6:1 SB296-2TH3.6 Vexta steppers. I know that I am going to have to weld and re-enforce the table, beef up the gantry, replace the X rails. I have a smaller cnc so I can machine any small parts I need.
I'm ordering this from Shopbot;

1 - 15304 Control Board w/ PRT V4g
w/4 Gecko Drivers 50v

2 - 002030 Drive Gecko G203

1 - 15167 Relay 5 Position 15A
(older Ctrl Bx may need 24v)

pwr supply (12547)

1 - 001756 Power Supply 24V 10W
Input 100-240V DRA10-24

I would like to put this bot together one time and make it capable of performing for me for a while. I'm not looking for top speed but need descent speed, torque, and resolution. Buying new steppers, etc. is not out of the question, everything is on the table. I won't be able to make it back to my shop to put it together for another six weeks but I'd like to make most of the purchases I need so I can get it up and running fairly quick. Any suggestions any of y'all can make would be greatly appreciated.

Thanks,
Rick

[bleeth]

Rick:

With basically new motors and a new 4g control box you will cut with pretty good resolution and be able to jog around 8-10 IPS. Cutting speed will depend on what you are cutting but will probably be in the range of 1.75 ips assuming plywood, mdf, or particle board without sacrificing accuracy. The limit on cut speed will come from the mechanics of the PRT gantry. I believe you have the bolt together gantry and z car. Regardless of motors that will be a factor in limiting speed. There were a lot of discussions back then (2004) regarding additional gussetts, welding, and outright replacing of the gantry and car.
The most straight forward and easiest to do is to weld the corners of the gantry and replace the uni-strut with something stiffer, like a box beam.
That should allow you to cut around 3 to 4ips. Make very sure it is correctly squared before welding!
If you find you need more speed and/or resolution then short of purchasing an all new Alpha kit the answer could be found here:
http://www.talkshopbot.com/forum/showthread.php?t=12709

Between assembling your new machine, getting used to it, and tweaking it as you learn the nuances you should be kept busy for a while!! Good luck and welcome to the community.

[donclifton]

I would not weld the gantry, even though you sq before the weld metal moves while welding. I know this has been discussed before but take some scrape angle iron sq and weld then put a sq on it. With both motors driving the gantry you don't need to weld.
Don

[curtiss]

If the two x rails are level, straight and parallel, the y car about has to run true above it. If the y car is square the Z will work properly.

For set up, I made a T-square out of some hardwood with a digital calipers taped to one end.

After getting one rail straight and level...

A shallow groove on the top of the T lays on one rail. The depth gauge on the bottom of the T will work as a "feeler gauge" and will show if the far rail is parallel to the first.

Everything is important but the x rails have to come first.

[rickwoody]

I plan on using some of the parts provided but building a heavy duty gantry and Z car. I asked to purchase a gantry from Shopbot but they said they only sell whole systems? I'll have to talk to Frank or Chris, the ladies don't seem to be as accommodating in selling just parts, and Frank seemed willing to build anything I wanted in a board. I'm probably better off just building something to get my Z's close together and lined along the x axis to keep max work area.
I seen a thread where Dave had rebuilt the x rails. How is that working out for you Dave? Looked like a pretty slick set up. Any other suggestions for rails?
With a souped up gantry, Z car, and rails, what kind of speed do you think I can get with the existing motors and the G4 Geckos without any gear boxes? If I swapped the motors? Used gear boxes? If I swapped out the motors, should I only swap the x's & y? Do you get much out of swapping the z motors? I would be happy, for now anyway, with 4-6 in/sec.
Thanks all for your help.
Rick

[bleeth]

The rebuild you mentioned has resulted in the smoothest running movements I ever had. Beyond the rails, of course, was the entire Gantry. The increased mass of the gantry has put a limit on the speed my original motors (same as yours) can run and my jog speed actually needed to be reduced a bit. To keep lost steps virtually at zero from that cause I now jog at 8 IPS and cut plywood at 3-3.5 ips. (Roughly double of the original gantry) Hence the next step of the gearboxes. You can get component pricing from Scott.
Consider that if you redo the x rails, put on a PRS gantry (which SB will sell as a unit), Get a 4g box, and buy new motors from Oriental and build gearboxes the question of why you bought what you have now would be somewhat logical as, after all, very little of it would be left!!
In my case, I had built my own steel frame originally, and now the entire top end is essentially a PRS (there are a few minor differences).

[rhfurniture]

The best mod I ever did on my prt was to add a second stepper/rack&pinion setup to the gantry carriage, one on each side of the gantry. I think the steppers you have are already geared 3.6 tapered hob, which is pretty good.
R.

[rickwoody]

I was toying with the idea of just building a machine and had priced Shopbot's "inventor's kit" and looked at other options. I can't afford a Thermwood so Shopbot was the obvious choice to run eCab's. The machine I bought is not what I needed but hopefully a good start. My logic is to have a comparable machine to the PRS Alpha for 75% of the cost of a new one plus have 2 z's and an A axis. I figure with the geckos, maintenence and replacement should be a bit less pricy. My logic is sometimes pretty expensive. I've been away from my shop for nearly a year now and ran into this unassembled machine in Northern California. Once I got the quote from Shopbot for the new controller with the six drives and relays for both z's and realized that the 10' table sides and rails wouldn't make too bad a centerpiece in my RV for the next six weeks (saving on shipping) I decided to purchase it. I'm pretty shopsick, and homesick, this little project kinda helps get me back a little sooner.

I definately want to put in x rails like your rebuild Dave. Do you have any info on the parts or suppliers you used? Also, when you fellows are replacxing the motors, are you just replacing the x's and y axis or are you replacing the z as well. I would think that the motors I have should be fine for the z's and a axis.

Thanks,
Rick

[Gary Campbell]

Rick...
One small flaw in your logic. You will NOT have a machine comparable to the current PRSalpha. Maybe a third, maybe a half, maybe more than half. Seriously, before your words convince the unknowing, and I am including you in the group because of your words, you need to make realistic comparisons.

There have been other posts that you were involved with that explained those differences. I will give the Cliff Notes: The 4G upgrade for the PRT adds a LOT. Very good package and a great upgrade for the machine to increase speed, torque and resolution. It does not bring the capabilities of the machine anywhere near that of the current PRSalpha.

There are a good number of us that use the PRSa and SB Link to cut eCabs designed cabs for a living. Many of us cut full depth 3/4" sheetgoods between 450 and 600 ipm. (thats 10"/second) and jog at 1500 ipm. Well beyond the capabilities of the 4G setup.

[rickwoody]

I stand corrected. I'm shooting to achieve about half the speed of an Alpha. I would be happy with that for a while anyway. Then maybe an upgrade. I will enjoy modifying the PRT for now.
Thanks,
Rick

[bleeth]

Have fun with your modifications. It can get very interesting. The most interesting part is that when you do one thing, you quickly discover that you need to do something else. It's a lot like taking over management of a plant that has used the same production system for ten years. Solving one bottleneck only unearths another! As I have pointed out earlier in another post:
A PRT with all kinds of custom upgrades is like a Studillac. Very cool, but it will never be a new Northstar Caddy.

[Gary Campbell]

Rick...
On your way back home, take a swing thru Northern Michigan. The view is good and I have a sweet little eCabs machine. You might get some ideas for your build.

[rickwoody]

The UP is a bit out of my way but I'd love to get back up there for a visit. I lived in Champion for 9 years, left in '05. I will be wanting to purchase your video on the SB link in the near future...but I think we'll use the mail.
I have a bit of room in my budget for the machine, but an upgrade to the Alpha, with 5 motors gets pretty expensive, 6 even more. And I was told by Diane that they will not sell a PRS gantry. I'm a little confused with that one. I believe with x-rails such as Dave's rebuild, a gantry from mostly scratch incorporating maybe a few parts of what was provided with the PRT, a y car of the same, and the G-4 controller, I should be able to get close to 4 in/sec depending on what I'm cutting of course. That should get me started. Replacing the motors with geckos if needed is fairly inexpensive.
I have a smaller machine now, and obviously know just enough about cnc'ing to be extremely dangerous! It is fun though...

Rick

[bleeth]

For my PRT upgrade I purchased the end plates and z assembly from SB. The rest I purchased as parts or metal stock machined in house except for the rack which I recycled. My Gecko control box was pre 4-g developed by Dirk. Reverse engineering it all without amything but a couple of PRS photos was interesting, as is the gearbox I am about finished with now.
Note Rick: The Geckos are motor drivers. The motors are Orientals. Your existing motors with a 4G (four Geckos) box will give you close to that cut speed after the gantry upgrade. Don't forget you will need an additional driver in the box for your 2nd Z.