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Author Topic: How to flatten table?  (Read 6512 times)

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How to flatten table?
« on: October 13, 2007, 07:35:40 PM »
Hey all!

I put together a great MDF router table - yeah it could be better but for my first machine I'm liking it!  The table was flat when I started, but I notice it has a slight bow to it now.  OK, maybe a major bow if you're measuring in thousandths!  Yeah, major!

I'm thinking I can just program a toolpath that will go back and forth over the entire surface and machine it flat, but I'm looking for recommendations before I do that...  I'm going to put another 1/4" layer of MDF on it as a sacrificial layer first anyway, so machining it flat won't hurt me any...

I'm also thinking of using the router to drill a hole in 4 known spots and I have bronze bushings that I will press into the holes and use 1/4" rod as indexing pins, so I can clamp pieces on the table and then move them a known distance, that way I can machine parts of "infinite" length just by indexing them forward on the pins...  Comments?

Offline Chaoticone

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Re: How to flatten table?
« Reply #1 on: October 14, 2007, 12:16:18 AM »
Yeap, surfacing the sacrfice sheet is common practice. Also, indexing holes will work pretty good too, depends on how tight the tolerance is I guess. Just make sure the work is held flat over the entire length. Reamed holes with dowels would be tighter.
Brett
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Re: How to flatten table?
« Reply #2 on: October 14, 2007, 07:01:37 PM »
Thanks for replying!

I used a drill bit to sink 1/4" holes through the sacrificial table into the moving table, then I took the sacrificial surface off and rebored the holes in the moving table up to 3/8".

Then I pressed in four bronze bushings with 1/4" ID, and now I can press the sacrificial surface back down on 1/4" removable pins.

My last question is what do people use to hold the sacrificial surface down to the moving table?  I don't have the setup for vacuum clamping yet!  Should I just countersink screws deeply into it and be careful not to hit them?
« Last Edit: October 14, 2007, 07:03:25 PM by tamathumper »

Offline Chaoticone

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Re: How to flatten table?
« Reply #3 on: October 14, 2007, 09:11:05 PM »
I wish everyone had a vaccum table, they are so nice. I don't have one either, maybe one day. Counter sunk screws are ok, like you said, be careful not to hit them. I would put them often and surface the table after you screw it down. How is your table mounted?

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: How to flatten table?
« Reply #4 on: October 15, 2007, 10:27:45 AM »
You guys are great - most other forums I wait days for a response (that probably never comes.)

I built a Rockcliff machine with unsupported rails for my first attempt, so the table has bronze bushings underneath that ride on two 5/8" rails.  I am going to be making some major modifications to it probably in the near future, but I want to make some chips first to see this thing in action!

Offline Chaoticone

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Re: How to flatten table?
« Reply #5 on: October 15, 2007, 09:51:32 PM »
LOL, I know the feeling, like a kid at Christmas.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: How to flatten table?
« Reply #6 on: October 16, 2007, 10:57:47 AM »
you may want to try shimming on top of the base below the  table top and then retighting more than likely you base is just a little out of square. Then cut top you might not have to take all that much off to get it flat again by using some shim stock. This is also done to square up machine to bases
Re: How to flatten table?
« Reply #7 on: October 16, 2007, 10:05:56 PM »
Thank you for your reply!

The table is a single piece, there is unfortunately no place to shim, although I might be able to shim beneath the sacrificial top it wouldn't buy me much, I can just screw it down and machine it just as easily.
Re: How to flatten table?
« Reply #8 on: October 16, 2007, 10:43:59 PM »
if it a one piece table don't shim iIs there a bow where it is high in the middle. You may have an issue that if weight is put on the table top it will flatten by itself. You may need to add some screw to pull it down. If you cut it now and there is a bow. when you put something on it then the table may not be flat after you cut it
Re: How to flatten table?
« Reply #9 on: October 17, 2007, 06:24:14 PM »
Double sided sticky tape is good to hold down your sacrificial sheet, also good to hold down parts as well.

You may have to seal bare/porous material for good adhesion.

Phil_H
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