Table Construction

[Bill Thorpe]

Over the next week or so I will be posting images of the PRS I am assembling. It occurred to me that there are not many photos on the Forum of the PRS. Hopefully folks who are just beginning the process will find the information helpful. Or perhaps the person considering a new machine would find this information useful in their decision making process. Comments and suggestions are welcome.

[Bill Thorpe]

This image is of the PRS table in the final stages of construction. One hint: Put the whole table together without tightening the bolts. Only tension the bolts finger tight or half turn of the wrench. It’s much easier to level, align and square it when it’s a bit loose. To align it I merely pushed, pulled or tap the legs with a short length of 2x4. It actually is quite easy to set up. As you tighten the bolts keep checking your measurements and adjust for any changes.

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Click on the URL below for a high-res version of this image. After the image loads click on enlarge to view a large scale image.

http://i243.photobucket.com/albums/ff30/billt_photos/DSC_1042.jpg

[rustnrot]

A thing I was told by another PRS'er was to "off-center" the legs on the table. In other words, since the router is not on the centerline of the carriage, it will always be to the left. Not really a problem but if you want your 4 x 8 sheet goods to be centered on the steel supports you need to have the left edge of the left leg(s) about 4" from the left edge(s) of the aluminum rail and the right edge of the right leg(s) about 10" to the right of the right edge(s) of the aluminum rail.

In fact, after I got mine setup you could actually move even more, i.e. less than 4" on the left side.

[Bill Thorpe]

Tom, I think it's covered in the manual but it's not to clear. I just set mine up so I had about 1 inch overhang on one end and the rest one the other end. (don't remember what the measurement is though) I wanted to have plenty of overhang on one end. Can you post a couple of images of your setup?

[dubliner]

I got my "feet" installed & got the first sheet bolted down to the table. The order I would advise is a small pilot hole from underneath through bolt hole, spade bit from topside, then full size bit for bolt from bottom. Its easier to center the hole from below. There are a lot of holes & bolts to install. Plenum sheet to be installed tomorrow. I'm thinking I might leave space between grids for T-track. I'm going to practice cuts on foam first. Say a prayer for me :-)BTW - I have about 18" of Igus chain left over if anyone is thinking of putting chain on their machine.

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[gundog]

I just got my Shopbot today around noon and I started putting it together. I have the table loosly together.

The instructions say to refer to the factory supplied drawing that comes with each machine for the spacing on the table braces. I have looked high and low but can't find any drawing. Can someone give me the spacing for a 4x8 PRS standard?

I am thinking they just need to be equally spaced. Maybe if someone knows where they might have put the drawing I will look again.

I am also wondering how far the end supports for the legs should be from the end of the extrusions?

Thanks Mike

[city_graphics]

I had the same issues. I found the drawings in the manual at the end of the assembly portion.

Your zero end, the first support is like 21" in.

[gundog]

Thanks another look at the manual and I found it. I will continue tomorrow. I am giving the manual a better read tonight before starting in again. I have 1 week to get it together and hopefully try to cut some parts. The whole week is dedicated to the ShopBot so I hope I get some of it figured out.
Mike

[waterwheelman]

Congratulations on delivery of your ShopBot. If I can be of any help, please give me a call. I'm just down the road. It'll be great having another ShopBotter in town.

[gundog]

Thanks David I sent you an email with my contact info. I lost your phone number. I only live about 3 miles from you.
Mike

[yankeepapa]

Group-

I just received my BT48. Suggestions on a table top material? Maybe MDF, but not sure how this will act during surfacing?

-David

[Gary Campbell]

David...
I prefer more humidity stable materials myself, but hundreds have used MDF with good results. Make sure is is sealed on all edges. MDF surfaces as good as any material out there, better than most.
Gary

[paco]

I'm considering changing my MDF support/spoilboard/vacuum grid to all Extira... but I still wonder if it's the best alternative both price and stability wise. MDF need to be surface every now and then because it swell and wrap over time. Main advantages of MDf and Extira is that it cheap and repairable if serious gouges happen.

[Gary Campbell]

Paco...
Extira is a much better alternative than MDF. Scuff it, wash it down and use epoxy to laminate it. Should be good for years.
Gary

[Gary Campbell]

Paco...
There are many other gluing options, than the epoxy, which is my favorite. This is from the mfgr:

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Gary

[yankeepapa]

Group, er uh, Gary-

Thank you for the feedback. As I'm still looking through my ShopBot manual (I've had my BT48 for less than 48 hours), I think I'll end up with three layers (i.e. factory metal "sliding" table, MDF, sacrificial board)? If only doing engraving (i.e. no cut-through), I'm guessing just the two layers (factory metal "sliding" table and MDF) would suffice?

-David

P.S. O.K., maybe this is obvious if I look at my ShopBot again, but what is the best way to attach the MDF to the factory metal "sliding" table? I can't really see using the ShopBot to drill holes, etc., as there's no sacrificial piece in place yet!

[yankeepapa]

Gary-

On a slightly different subject:

my new BT48 (pre-assembled) has the table (x) motor mount "rotated". The mounting bracket isn't square with the table frame. However, there seems to be a stop/adjustment screw that has been set to make the exact amount of rotation desired and correct.

What is this for? Maybe the table has already been "adjusted" properly?

-David

[Gary Campbell]

David...

In your case, it sounds like the 2 layers you describe will work. You might want to use the Bot to mark (drill .030-.050) holes for countersunk bolts into the metal table. Make sure that you clear all movement areas. You will them be able to mark or drill your MDF for bolts (maybe nylon?) to fit on the metal table. This should make replacement a snap in the future.

I am sorry, I do not know enough about that configuration to be able to help you. You should email SB tech support for the best answer.
Gary

[dana_swift]

David, you can (and should) use the shopbot to create the mounting holes on the sacrificial board, all you have to do is make a sandwich of "scrap" below what will be your sacrificial board, then you can drill the baseboard using the machine.

Be absolutely sure your table is square before making these cuts. My BT32 did not come square, and I probably spent two or three days tweaking it to square. You can get within a half a thousandth of square with just a little persistence.

Since I got my BT32 running I have made a fixture out of UHMW that holds a dial indicator and rotates over each of the pre-tapped screw holes in the table to guarantee the squareness. If you like I will take some pictures, the time you spend making the machine absolutely true will be worth the extra effort.

D

[yankeepapa]

Dana-

I'll email you off-line, as this may be more than this thread calls for. (Yes, I would welcome pictures.)

-David

[yankeepapa]

Dana-

Oops. I don't see your email address. You can contact me here or offline: dcm(at)c-sw(dot)com.

TIA

-David

[dana_swift]

David- you have mail. Check your spam folder if you dont see anything.

D

[dana_swift]

David- I keep getting DNS unresolved bounce messages from dcm c-sw com (at and dot not shown). So I put some pictures here..

What I did is drill two holes in a peice of UHMW, the hole geometry centers a dial indicator over a bolt. Hopefully the picture helps show this.


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Then I can "loosly" bolt the dial indicator over any hole in the BT-32 table grid. I chuck up a peice of 1/2" round smooth stock about 3" long into the half inch chuck of the router. Then move the router to above the hole the DI is located in using M2 commands.


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Between these photos you can see the dial indicator pivots over the vertical bolt. When the router is directly above the bolt the dial indicator will not change as you rotate the UHMW.


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(Note in these photos I am actually setup to make parts using the vacuum fixture you see.. if I were really doing the table squareing I would have nothing on the table at all, no vacuum fixture or spoilboard. I just took these pics to give an idea of how I do my squaring.)

Once above the hole I slowly lower the router using the K keyboard interactive mode. Use caution, you must pull the dial indicator probe out of the way during this process! Then change the position of the router using M2 until the dial indicator can swing completely around the router moving no more than 0.001 inches.

Note the position of the X and Y values on the SB3 readout.

Do this again at a position along the gantry motion (BT default is to lable this as Y (I consider this as X in my setup)). Now you can measure in thousandths exactly how square the gantry is with respect to the table.

Then I loosen the bolts holding the right side of the gantry to the extrusion. Using a furniture clamp I put a small amount of pressure on the gantry to move it. See the photos.


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Knowing the thread pitch on the furniture clamp lets me know about how far to turn the screw to get the amount of movement the dial indicator is calling for.

It is an iterative process, the first time it takes forever, but you will check this every month or two to be sure it is where it belongs. When the average temperature of my shop changes by about 10 degrees F I recheck it. It is usually different from where I set it by 0.001 or 0.002.

So measuring two points on the table using the simple dial indicator fixture allows very accurate squaring. However CHECK YOUR TYPING using the MX, MY or M2 commands.. you can drive the router into the dial indicator and destroy it! So far I haven't done that.

You could use the "center in hole" routine provided by shopbot, but that requires a fixture like the superzero, and I don't have one of those, I did have a dial indicator and some UHMW.. so this is what I did.

Once the table is 0.001 square you can get some real precision from the SB. If the table is not square it doesn't matter what you do, you will not get precision!

D

[yankeepapa]

Dana-

Thank you for the photos and information. My email address is valid, but some systems on the 'net balk at the hyphen (i.e. "-") in my address. (The hyphen is a valid character, but I guess some software developers along the way forgot that.)

Anyway, thank you for the information.

-David "thinking about a new email address" Matthews