Checking for Square...

[thecabinetconnection@earthlink.net]

Ok, it's me again. The fine folks at Shopbot said that one good way to check for square for x,y & z was to pocket cut a rectangle using a large cutter and use calipers to measure the dimensions of the pocket.

First, I went to ms 15,5 and tried an air cut. Now, today, I have been building solid surface tops using hand routers. So when this thing took off and air cut a 3.00,3.00 rectangle I 'bout jumped out of my skin! When I ms 15,5 didn't I set the speed for xy to 15"/min and z to 5"/min? My gosh the thing was zipping! Or is 15,5 really 150"/min and 50"/min? I slowed it down to 5,1 and used the 1.25" spoilboard surfacing cutter to cut the 3.00, 3.00 rectangle to a depth of 1/2" using 2 passes.

The results were that x,y square appear to be close but the sides closest to 0,0 was 1.5mm deeper than the opposite side. That would indicate that the spindle is leaning towards 0,0 a smidgen right?

Now, I had read somewhere that the accuracy was not linear over the distance of the table, right? For instance, when I square my sliding table saw, if it's out .010"/12", it's going to be out .09" over 9'. But if the pocket hole rectangle is out .010" over 3", it's still going to be out .010 over 60". Is that right? I may be losing it. It was a hard 15 hour day....

Thanks for your time.

Chris

[gerald_d]

Chris, those settings are inches per second. You need some sleep.


Don't worry about z square until you have surfaced the table at least once.

For x,y square, I screwed 4 blocks of scrap to the table, as if they were emulating the 4 corners of an 8'x4' board. Then measured the diagonals of the "board" until square.

Accuracy will be linear if your rails are straight and your table is flat. The real starting point of setting up any squareness, is first to be completely anal meticulous about straightness.

[kerrazy]

Watch your speed, if you are running 15"/per second and rack your machine your asking for a world of trouble. The most you should run it is a jog speed of 4.5 and even than it may lose steps.
Cutting speeds can be as high as 2.5/sec but be prepared for tear out and potential lost steps as well.
I run sheet goods @ 2//sec and this seems great.

[rgbrown@itexas.net]

My method of checking square on a machine I am not sure about is to take a piece of "scrap" sheet material, bore 1/4" holes in a minimum of three places, say 2,2; 2, 26; 14,24. These holes go through the scrap sheet and into the top.

I filp the sheet over and with dowels or bolts or? I locate the part "in reverse". The hole that was at "14,26" will be of double the amount out of square.

On the initial layout of my nmachine, I made a large beam compass and built a "line perpendicular to a point" projected across the "X" rails and scribed a line. I still use an offset of that "line" for my square check.

[windsor@muskoka.com]

When I built my wood table I surfaced the tops of the crossers that left a 1/4" deep pocket . When I installed the spoilboard I used 3/4" mdf and made sure that the sheet was sqare by measuring the diagonals of the sheet ( it isn't always square ) . When I screwed down the spoilboard I made sure that it was tight to the sides of the pocket to ensure that it was parrallel to the x axis . To check the squareness of the y axis I just used the end edge of the spoil board as my square , and used feeler guages between the board and a 1/4" rod chucked in the router to fine tune the y car .

[thecabinetconnection@earthlink.net]

Great advice on checking square. Geez, and I thought setting the slider up was tedious...I can be very, er, meticulas. At first, I tried leveling the machine with a machinist level but that drove me nuts. So I went with a 4' level.

Well, inches/second. That explains my reaction. Amazingly, the calipers showed that it was about as close to exactly square on the 3x3 rectangle as I could measure. I'll do a check on a very large rectangle. You know, even at a speed of 5,1 the cut was actually pretty good! I did have some variances on depth of cut when measured around the perimeter of the pocket cut. The excessive speed could have alot to do with that. I'll try that again at a more reasonable speed.

Gerald, if I surface first, and the z-axis is out, won't it leave a groove on every pass? Or is that why I should plane the table, then adjust the z-axis and then recut the table the second time?

Using that 1.25" table surfacing bit, what cutting speeds should I be using?

Thanks,

Chris

[kerrazy]

Chris if you follow the diretions laid out in your manual ( the white binder covered in sawdust) it will tell you step by step how to surface plane your table.

your inital pass should be about 1.5 inches per second and when you have the desired depth you could turn it up to 2.5 inches per second I would hesitate any quicker again to avaid missing steps. at this speed you really should be removing only an eigth of an inch or so. I find you may need to do this roputine regularly once every few weeks in the summer as the humidity changes. So keep the info handy
Dale

[thecabinetconnection@earthlink.net]

Dale,

I have been trying to reference the manual as much as possible. I didn't see the section on surfacing the table. I'll look for it tomorrow. Before I do it though, I'm gonna figure out the z-zero issue.

Thanks,

Chris

[gerald_d]

Chris, for squaring the z-axis, you have to have a reference plane - otherwise, what are you squaring it to? Yes, if you surface the table before squaring, you will get saw-tooth ridges about 1" apart. But they will be consistent ridges and your measuring tools will easily span the ridges.

You don't need to surface the whole table for the first round. You could even put down a small piece of scrap (about a foot(300mm) square, seated firmly) for the surfacing/squaring exercise.

Also see these threads on trammels:
Thread 1 (http://www.talkshopbot.com/forum/messages/7/1172.html?)
Thread 2 (http://www.talkshopbot.com/forum/messages/7/1291.html?)

[kerrazy]

Chris page 58 of your manual should indicate something like first project: Surfacing your table.

have a peak and follow the instructions as they are very detailed.

Good luck,
Dale