Table Surfacing

From Shopbot Wiki

Surfacing your Table Top:

Having a flat table top is crucial when you're cutting parts that are thickness-critical. It's a pretty simple job, and generally needs doing every couple of weeks if you have any kind of temperature or moisture changes in your shop. Moisture is really the biggest problems, and if you can seal the edges of your top with paint or epoxy, you may save yourself some work in the long run.

To speed the process up, select the largest bit you can find to surface the table top and chuck it in the router. 1" diameter will work fine, but if you can find a bigger bit it will take less time. Now type VC to bring up the cutter diameter fill-in sheet and let the software know what size bit you'll be using. After typing VC and hitting ENTER, you'll want to change the first setting in the fill in sheet that pops up, the one that says "Cutter Diameter". Change the number in the first section to your new bit diameter; it's probably set for the default which is .25 . When you're done click the OK button at the bottom. NOTE: Remember to change it back to the correct size for cutting your parts when you are finished surfacing.

How to Flatten your table top...the easy way:

The current ShopBot Control Software includes a Table Surfacing Virtual Tool when it installs. It can be accessed from the "Tools" menu or by typing "TU" in the command line. The Table Surfacing Tool works by writing a custom "CR" command which is one of the built-in ShopBot commands that is used to "Cut Rectangle". The Surfacing Tool makes the process of customizing the CR command easier by putting a Windows interface on filling in the parameters.

Surfacer Virtual Tool
Surfacer Virtual Tool

How to Flatten your table top...the manual way:

You can manually fill in the settings for the CR command if you would prefer. Move the tool until the bit is centered over the 0,0 point on your tabletop and just touching the surface, and use the Z3 command to zero your tool there.

The next thing to do is to find out how un-flat your top really is. An easy way is to make a series of diagonal cuts, dropping a little bit each time until the bit cuts all the way across. With the tool at the 0,0 point and the bit at the surface, turn on the router and run the tool to the opposite corner by typing J2, 96.0, 48.0 (or whatever size table you have)

Because of moisture absorption the edges will be probably be high and the middle will be low, so there will be a section in the center that the bit didn't cut. If so, move to the lowest spot, lower the bit a little with the Keypad (with the router still running) until it's just cutting into the table top, and then type ZZ to make this the new Z-axis zero point. Now type J2, 0.0, 0.0 to return to the home position. If it still doesn't cut all the way across, just repeat this process of lowering and cutting diagonals until it does.

To actually flatten the table you'll use one of ShopBot's built-in commands; CR for (C)ut (R)ectangle. To be sure that you're doing everything right before you actually cut, type SP to change to preview mode. Now type CR and a fill-in sheet will appear; you'll need to make a couple of changes to this. 

An example fillin sheet for the CR command
An example fillin sheet for the CR command

When you have the fillin sheet completed, click the start button to draw the Preview. Your preview screen should be completely full of concentric rectangles that get smaller and smaller until the whole surface is covered. Now you're finally ready to true the table. Go back into cutting mode by typing SM, then with the router on move to the corner by typing J2, 0.0, 0.0 ( your Z-axis should still be at 0.0, which will soon be your new table surface). Type CR again and make sure the fill-in sheet is the same as before, then click Start

When it's finished cutting you'll probably need to hit it with some course sandpaper to knock down any ridges between passes. And if the surface is saw-toothed, you'll need to square the Z-axis to the table top. Instructions for doing this are included in the ShopBot assembly manual.

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