View Full Version : Table design to permit 5' wide material in PRT96?

02-17-2002, 02:04 AM
Hi, I'm a ShopBot newbie who's been lurking here for about a month, and before I take the plunge (a little router humor...very little), I'd like some opinions about a custom table design.

My question is:

Q: The largest sheet that I normally machine is 5/8" x 60" x 84" Melamine, however, the cutting path is well within the range of a PRT96. So, can the steel table plans be modified so as to accept the wider sheet, provided the PRT96 tool has the standard 64.5" x 120" mounting area?

A: My hypothesis is to invert the legs and sides, and increase by 4" the size of the cross members and end supports.

Please take a look at my quick sketch of the default PRT96 table and the modified unit by clicking on this link: PRT96 Steel Table standard and modified views (http://www.cleanaccess.com/sbtabmod.gif) and let me know what you think.


02-17-2002, 11:19 AM
Hi Rick, sorry, but the SB's x-axis motors hang below the rails and they occupy the space that you want to "steal"

02-17-2002, 11:33 AM
However, once you know how much space the motors really need, a solution should be possible.

02-17-2002, 12:17 PM
Topic: The X-Files :^)

Many thanks, Gerald, your input is very helpful. Sounds like I would need to extend the table in the "x" direction and move my legs further apart so that they do not interfere with the x-axis motors within the 102" of right-to-left travel. Of course, that would mean adding a support leg directly under the center of the table (not a bad idea anyway).

Another approach would be to design more of a pedestal style base beneath the 10' x-axis side rails (and y-axis cross members).


02-17-2002, 12:38 PM
Support legs under the centre of the beams are a good idea.

Actually, you only have to shorten the side-mounted legs a bit so that the motors can pass over the top points. If the legs are shortened, you can weld gussets from the bottom of the beams to the sides of the legs to compensate a little.

Are you planning on purchasing a table kit from SB? If not, are you going to weld or bolt your table together?

Sorry that I cannot follow through on the X-files theme, it wasn't that big here

02-17-2002, 12:47 PM
Sounds like a decent fix, thanks Gerald.

I'll be building the table from scratch, and I was planning to bolt it together in case I had to make adjustments later.

A clarification: when I said in my initial post that, "the cutting path is well within the range of a PRT96" I didn't mean to cut any wider than the maximum 50" that the PRT96 is capable of cutting. In fact, my patterns do not exceed 44" from y0. It is the sheet size I am working with that is the problem.


02-17-2002, 01:12 PM
Hi Rick,

If you haven't ordered your ShopBot yet, why not get it with a 5' y-axis instead of the standard 4'? Don't know how much price difference there is, but you'll be able to cut the full 60" width of the sheets if you ever need to and also 5x5 Baltic Birch panels.

Just a thought,
Bill Young

02-17-2002, 01:36 PM
Hiya Bill,

Thanks for the response (on a Sunday yet!).

My company manufactures "Air Showers" for cleanrooms, R&D, pharmaceutical manufacturing, defense, and bio-tech industries. The Air Shower serves as entry into a restricted area where contamination control is critical. Our finished units look like this: Typical Air Shower (http://www.cleanaccess.com/as4dr.html).

We offer our product in aluminum honeycomb aircraft panels, CR steel, stainless, and Formica laminate over Melamine board. We would be using the ShopBot to cut the circles for the air nozzles and the rectangular cut-outs for the return air grilles. I'm sure we'll think of many other applications as we become experienced with the PRT.

I was first considering the 5'x10' unit, but looking through our shop drawings I realized that none of our patterns are wider than 44" from y0, and no more than 68" from x0. Also, we have a room which we will dedicate to the tool, and going up to the next size might cramp things a bit.

I'm still open, however. Right now I'm more interested in "can it be done?" so I can make a decision next week on which machine to purchase.

What is the current lead time on these machines?

Thanks a bunch,

02-17-2002, 03:22 PM

I'll ride along with Bill and suggest the 60" tool. It is real nice to be able to cut all over the sheet of material. I curse myself every time I cut a sheet of "Baltic birch" so it will fit on my old machine. But, 1/2" 5x5 sheets are about $0.70 a square foot while 4 X 8 sheets are over $1 a square foot.

Loose pieces will need to be relocated to get a new 'zero'. This move is avoided of the sheet remains whole until the parts are all cut. Then again, if you don't need the capacity, you don't.

Ron Brown - wdyasq@yahoo.com (mailto:wdyasq@yahoo.com)

If Stupidity got us into this mess,
then why can't it get us out? - Will Rogers

02-17-2002, 08:15 PM

Thanks for the input...I'll most likely shell out the extra grand for the 60" tool, assuming it will fit the room I have allocated for it. Worse case I can look for a another spot in my shop, I suppose.


02-18-2002, 02:37 AM
Hi again Rick

A standard PRT96 (4' y-gantry) is already 77" wide over the x-motors, plus you need space to walk right around. You want to cut aluminium as well, so you want a good strong gantry, and I will be hesitant to buy a gantry that has simply been extended. Maybe the longer gantries are made from a heavier section?

If you want to stick with your original idea of reversing the long rails, then you need to trim 2" off the top of the legs and then bevel the remainder away at 45 degrees. The motors have changed slightly since my model, so these dimensions must be double-checked.

02-18-2002, 10:38 AM
I would guess that the gantry components are the same for all units, just extended in size; I'd be interested to know for sure though.

Same deal for the tables: the 4'x4', 8'x4', and 10'x5' units are all identical (save for the overall dimensions and added cross members). It's not like they go from a 6" rail to an 8" rail...all the tables have 6" rails. So, they have engineered a table design that suits the largest size unit, and then used the same design and components in the smaller tables. So, if you buy (or build) the 4'x4' table, it will be extra beefy, having the same 6" rails that the 5'x12' table uses.

I like your idea of trimming and beveling the legs. First thing I'm going to do is measure out my shop for possible placement of the 'bot. I had a separate room I was going to use, but if I do, I will definitely have to modify the table and use the 4'x8' unit.


02-19-2002, 10:29 AM
Virtually all components, including gantry members, are identical for all units. The 4' and benchtop tools are undeniably stiffer than the 5' ones, but it won't prevent you from cutting aluminum or anything like that. The surface quality isn't perfect on aluminum regardless, so any quality differences between the two widths will probably be hard to measure.

Grant Bailey
ShopBot techsupport
grant@shopbottools.com (mailto:grant@shopbottools.com)

02-19-2002, 05:23 PM

Sounds reasonable, thanks for the info. I'm still thinking about which size to go with--there is a 11'x15' room with double-doors in the back of my shop that I could use, so the more compact the PRT the better. The advantages of the 5' unit may outweigh the space issues, however, and I may want to place it elsewhere in my shop.

Are there plans for the wood version of the tables anywhere? I'm just curious to see them, and all I can find on the site are steel table plans. I've downloaded all the steel table plans and studied them. The cost for the 6"x8.2# channel, the 3"x5", and 2"x2" angle is less than $200 total for the 5'x10' table, which isn't bad at all. It looks pretty labor intensive though.


03-02-2002, 06:52 AM
After much research, I chose not to build the wood table. Instead I built my own table out of 2 by 3 1/4 inch angle and 10 in channel for the sides and legs. A little bulky to work with but very stable and ridgid.....the key in using channel is a little angled washer that you can buy from McMaster Carr. My table will cut 50 inches by 110 inches... I just bought a couple more feet of gear teeth and extended each axis. The cables reach just fine. I put down two sheets of melamine coated fiberboard for my surface and have a 12 inch travel in my Z axis. So the modification is quite simple .....just build the table to handle the size. But DO build it from steel to avoid the humidity and other similar issues that you find with large pieces of wood structure......

03-02-2002, 06:59 AM
Thanks Thomas, sounds like a robust table. By the way, did you (or anyone else out there reading along) use vibration isolator mounts? Seems like that would help dampen noise a little, but I don't see anyone mentioning them.

03-02-2002, 12:06 PM
I've used adjustable vibration isolators from MSC from the start.No vibration at floor,no creep & they give you a much larger surface for weight distribution.

03-03-2002, 09:42 AM
To follow on from Thomas' mention of an "angled washer". . . . . .

Steel channels and I-beams are available in two different styles of flange profile; taper and parallel. If you have to bolt through a tapered flange, then you need a tapered washer (http://www.almetal.nl/techinfo/wsh/wd6917.htm) to compensate for the taper, stop the bolt from bending and allow the nut to turn freely.

A tapered washer is square around the outside and has one serrated face. It should only be installed in one particular orientation, otherwise it makes the problem worse.

What we had a habit of doing in the steel construction industry, was to drill the hole in the beam flange way oversize because the taper washer can cover quite a large hole. When everthing was bolted in the right place, then we welded the washer to the flange with small tack welds at each of the 4 corners.

But it is easier to use parallel flange channel from the beginning. . . . . .

03-03-2002, 12:58 PM

Thanks for your helpful comments. Are the vibration isolators used at the floor? only at the floor? Pls advise. Also where/who is MSC. Many thanks for any info!

03-03-2002, 01:27 PM
Jeff, do you have some contact info and perhaps a part number for the vibration isolators that you are using? Thanks.

03-03-2002, 09:42 PM
MSC is Manhattan Supply Company. I have included links to two other on-line little gems that might may help. J&L Industrial has several 'outlets'. McMaster-Carr is the 'mother-lode' of on-line supply shops IMO.




Ron Brown - wdyasq@yahoo.com (mailto:wdyasq@yahoo.com)

If Stupidity got us into this mess,
then why can't it get us out? - Will Rogers

04-30-2002, 08:40 AM
I built a 60 inch wide machine. When I attached a laser to my cross carriage and shot it on the wall, I was extremely dismayed to find that I had almost .20 inches of sag in the middle of the travel. By using a 3/8 rod, and using it as a bridge truss affair, I was able to tighten the threaded nuts that I placed on each end of the rod and virtually eliminate the sag. Was a little time consuming but really did the trick.