Table Leveling

[joe]

Hello Folks,

Over the years I have found it necessary to continually re-level my table top. This usually happens when I'm in a real rush, on a critical job.

I'm considering fabricating an aluminum base, simular to the high dollar CNC's. My thinking is this; Trupan, which I love, continues to swell and move around, even when edges are coated. I'd still use it when a I need a sacrifice board, but on those critical cuts, I could rely on a aluminum foundation.

It would seem easy enough to make a base from a couple of sheets of diabond, with interior spacers, for a vacuum. A nice hole patern could replace my porus Trupan.

I know there's a big flaw in my thinking so, would appreciate you guys suggestions.

O, by the way, my table frame is from 4"X6"X 1/4" I beams and weight at least 400lbs, so I know it's not moving.

Joe

[gerald_d]

What is this "diabond" that you refer to? Google tells me that it is related to ceramics with diamonds used for coating dental drills, etc.

If you are talking of some aluminium type sheet, screwed to your steel bearers, you would probably have get alu about 1" thick if you want it to be stable for vacuum and "those critical cuts". Or, a very solid "interior spacer".

[ron brown]

Joe,

I drew up - but never built, something similar to what you are proposing. I had different thoughts on material.

I had planned on using baltic birch with an "egg-crate" style seperator. I would give the parts two coats of epoxy before bonding it all together. This would seal the wood and be a vacuum plenum also. I planned on a "sacrificial" top of baltic birch above that.

Well, I went to Ohio and have had a couple of years to think about it. I would change the base panel and possibly other parts to the aluminum clad panel - I can't pull the name right now - and use "Alumathane" to coat the wood before assembly.

BTW - my "Baltic Birch" tops have been much more stable than the MDF I origainally used, pieced and replaced a few times.

Ron

[joe]

Gerald,

I gave you an incorrect spelling for the aluminum it's DiBond. It comes in 2mm 4mm &8mm thickness in 4'X8' and 4'X10' deminsions.

Cost is about $100 each. Most any sign supply house has it. Very popular in the sign trade as an exterior backrgound and machines very easily.

J

[joe]

Ron,

I'm sure tired of flattening that table.

I not crazy about sheeted aluminum for my base because it can be floppy. DiBond and Alucobond are very different. There flat and stable.

Should be able to seperate the top and bottom sheet with 1" aluminum tubes.

J.

[gerald_d]

Joe, your 1" square-tubes would probably have to be around 4-5" apart if you don't want to see significant ripples after applying a good vacuum. (based on what I read about Dibond). I can't think of an obvious way to attach the sheets to the tube, other than double-sided tape......

[ron brown]

We may be talking about the same panel - "Alumalite" , "Econolite" and "Omega-lite" are all aluminum panels with a corregated plastic core. Very stiff and light. I think DiaBond is the same or similar stuff.

Ron

[joe]

Ron,



Alumilite and DiBond are made by the same manufacturer but different in that DiBond and AlucoBond have a solid core. They are much tougher and cost is about twice.

Not sure I would use Alumilite for the top surface as it is easily dented. AlucoBond would be the best, but is very expensive for an experiment.


J

[fubrain]

Hello everyone,
My table is very simple and stays pretty flat continually. What I have is a 3/8 piece of steel as my table base attached to my bot frame. Then I have a framed in opening (plentum) with runners every 6 inches to support the top sheet. The top sheet is 1" pvc with 1/8 holes every 3/4 of an inch for suction. I end up with 4 seperate zones that can be turned on and off separately. The air space under my top sheet is the table size x 1 inch thick, Which gives me plenty of volume of air to pull for suction. (The secret to successful hold down with a shop vac.) I use a 6.5 horse ridgid and you cannot move a sheet down to 12x12 in size, also being that it is steel and plastic humidity plays very little in table change
Hope this helps! ROSS

[joe]

Gerald,

A 2mm thickness sounds as though it would be flexable. Believe me, it isn't. I think you could put struts about a foot apart without any problem. Of course I'm not running a $3000 vacuum pump either. Even then it might work ok.

My vacuum is a double Jet 2 HP.

I think 3M's HVB tape would be a good choice to put the panels together, or silicone glue. You could use Gorilla glue if the edges were sandes.

J.

[mikejohn]

How often does one have to 'level' a table?
..............Mike

[gerald_d]

It depends on how often you run a cutter into it, or how much it changes with the seasons. In our case it is between 1 and 6 weeks - it takes 20 minutes.

[fleinbach]

Ross

Do you use a thinner spoil board to pull through to keep from having to resurface the more expensive 1" PVC?

[gerald_d]

Joe, believe me 2mm is very flexible. My 4-5" spacing estimate is for the thick stuff of 6mm with a good shopvac.

I think a "Jet" is what you guys call a "dust collector". Using that and thin 2mm "foiled plastic", I would stick with the 4-5" estimate.

But using thin foils of alu, LDPE plastic inners, D/S tape, solid alu tubes on steel cross members seems way too complex and fragile. This is not going to give you anywhere near the "aluminum base, simular to the high dollar CNC's" that you are seeking. The $$$ alu tables are very thick, solid and not mixed in with other materials.

[joe]

Frank and Gerald,

I do quiet a bit of V carving and area removal of letters on my signs. To render a deliclate script when V carving, a flat base is necessary. No sacrifice board is need here but, one could be used when doing profile cuts.

When I purchased my PRT, I had never even stood in front of a CNC. Kind of like a blind date. Guess I got lucky. The bed on the CNC's I saw in magazine looked like ribbed aluminum. Owners of these machines must remove sacrifice boards much more often I than I do. Guess I should move in that direction. Would love to find a good cheap sacrifice board to trow away more often and eleminate much leveling.

When I saw Brady Watson neat engine turned swirls, "Experiment in Aluminum", it all came home to me. You probably need a very flat base to do that type of work.

I can see real possabilities for this type of product in my business.

J

[fubrain]

Hello Frank,
I dont use a spoil board, for items that are cut out to table depth. I initalize to the table top - about 4 thousanths from surface this does 2 things , saves my table top and leaves a labrynth to hold small parts together when cutting multiples. Sometimes when I have to cut many small parts (1 x3 inches ) ill use transferite transfer tape on the back side that acts as labrynth. I initalize to the tape surface and the vac holds the tape and the tape holds all the parts together when cutting.
sounds confusing but its easy. Depending on the size of the item ill use a down cut if its small
ROSS ( TAPE IS ABOUT 50.00 DOLLARS FOR A 24X 100YD ROLL

[fleinbach]

Thanks Ross

I'm picking up as much info as I can to do my vacuum table. I am gathering as much information as I can trying not to overlook anything. I hope to get it right the first time so I don't look back and say, why didn't I think of that.

[Brady Watson]

Joe,
Actually...the AL was held down with weights and ONE screw...LOL! I was too lazy that day to make a little vac mask to hold it down properly. Even the engraving was done on my beat MDX spoilboard.

I have mixed thoughts about an AL spoilboard. Yes it is more stable than any of the wood options out there...but you will WANT to put a wooden top on it to spoil...and there goes your super flat top. I suppose that you could always have a nice flat top if you just resurfaced the spoilboard at more frequent intervals. I have seen many bots where the spoilboad flatness is a moot issue because the Z-axis is out of alignment or they are still using a zero plate at the default .131" when in actuality it is .121 etc.

Ross,
Can you post where to get the tape and part # ?

Frank,
You may find that seperate vacuum jigs are more useful than sucking down the entire table. If you process large sheets all day long, a vac table makes sense. Since I do a lot of one-offs and smaller items, I have found that a dedicated jig (or one say 2 X 3' in size) is much more useful. I create vac 'masks' that can be swapped out using a common plenum. This way I don't have 42,000 jigs all over the shop. Does that make sense?

-Brady

[fleinbach]

Brady

I have been thinking over this delima for several months now. I thought about the masking after talking to Jeff Guinn. He had some very good tips on masking and the fact that a very small pump was enough if masked carefully. But I cut mostly full sheets and almost no 2 are alike so masking becomes a bit more of a problem.

Off course my primary use of the Shopbot has been building Home Theater Rooms. That is pretty much over. I removed the model from the furniture store in Rockville just this weekend. It lasted only 15 months. I did get to build 6 theater rooms while it was there though. Why it was removed so soon is a personal matter between the furniture store and the company that made the original deal with them. By the way this was the first parts I ever cut with the Shopbot. I may still get to build another room but this was my best source. I will now be using the Shopbot to build specialty items for my Home Improvement buisness as needed or designed.

I will definatly at some point still add vacuum since I'm getting real tired of ruining bits on screws. Up until last week I had only destroyed 1/4" bits but then I put a brand new $50.00 bit and was positive I knew where to put the hold down screw. Yes I know there are many ways I could have been more certain, but this is the price you pay for being positive you can remember the size of the part you layed out yesterday was 16" and the material is 18" so 1" from the edge is safe. WRONG! The part I layed out was 16" X 18"

SO anyhow eventualy I will have a vacuum system.

[richards]

Frank,

Welcome (I think) to the "how to destroy a valuable cutter quickly club". It's happened to me more than once, which is why I use a vacuum system.

On large parts, I use a Fein vacuum and a vacuum mask. If the parts are large enough and the depth of cut reasonable, it works.

On smaller parts, I use a GAST pump with a vacuum mask and weather stripping masking. It works reasonably well.

When I'm using full sheets and a combination of large and small parts, I use the Fein vacuum with a vacuum mask and tabbing. The tabbing keeps the small parts intact and the vacuum mask keeps the large parts intact.

It's all somewhat of a pain because I would really like to cut all sizes from full sheets in one pass. So far, I haven't found a way to do that.

-Mike

[richards]

re: table leveling

Here in Utah (desert conditions - low humidity), I've been surprised at the changes in my spoil board (MDF) over the last few months. It seems like it only takes a few hours to get a measurable change. Re-surfacing the table doesn't seem to cure the problem because the sheet goods that I'm cutting vary in thickness depending upon the humidity.

It doesn't seem cost effective to use an aluminum table top (which is assumed to be perfectly flat) when the sheet goods have enough variance to negate the flatness of the aluminum table top.

[bleeth]

Frank: In the meantime try marking your screwhole locations on your drawing plan. I've been told some guys lightly clamp the piece and run a drill routine for the holes before they cut the parts.
Too bad about the retail outlet-I really liked the designs in your rooms and hope you get to do more (if you want).

There is an outfit in Texas called raptor that made a plastic pin for their own nail gun and it just occured to me it may be a good replacement for screws. They do staples too.

http://www.raptornails.com/english/firstframe.html

Dave

[bill.young]

and plastic drywall screws

[bill.young]

I take that back...they USED to sell polycarbonate drywall screws but they aren't listed on their web site any more.

[fubrain]

BRADY,
The transferite tape is sold in 100yard lengths x pretty much any even width you would like. There are a couple of brands, I use Transfe rite and conform both high tack. The cost is around 50 dollars for 24x100 yds. The transfe rite can be bought at any sign supply outfit. ( transfer tape is used to move vinyl graphics from there backer to a substrate)The code for the transferite is 582-u. Im not sure if that is high tack or normal but that should get you going. GOOD LUCK! ROSS

[joe]

Bill,

I was very interested in the Raptornail system until I saw the price of the gun. A year ago it was about $200. Not bad if you needed it for other uses.

Mike R.

The purpose for a level table top, that stays that way, is for those jobs that require it. A spoil board on top would still be necessary.

Joe

[fleinbach]

Dave

Yes, I have used the method you describe many times. But I have always had a bad habit of taking shortcuts and not taking the time to do it right. I know the old saying "If you don't have the time to do it right, when will you have the time to do it over" But somehow I still get in a hurry. You would think I would have learned something in the past 58 years.

[Brady Watson]

Thanks Ross!

So far I have been getting by with carpet tape...it's nice to know that I can get something that wide.

-Brady

[gerald_d]

Joe_C, out of curiousity, how did you plan to "level" your aluminium sandwich table to get it parallel to the SB's rails?

[bleeth]

Frank: By this time what I have learned most is how to say "How did I make that stupid mistake again!" hundreds of different ways from "aaarrrgghh" to "zzzaaaapppp"

[lto]

Hitting screws is not a problem if their locations are in the cut file. In Parts Wizard I will place 1" circles wherever I want a screw. In shopbot edit I'll add a Jog line to move the tool out of the way after drilling shallow holes with whatever bit I may be using. Following this add a PAUSE to allow screw insertion time. Continue running file and stand there and grin as the cutter moves toward the screw and stops just an eighth inch away from the head. I hope this helps someone as I learned it after finding that I'm not very good at guessing at safe locations.

[joe]

Gerald,

I don't thing the rails are too important in this process. It's the relationship of the router to the bed.

Moving the router to all four corners and adjusting with shimms should do fine.

I must admit, this is an experiment, which if it fails there is still the good old wood and glue.

Joe

[matt p (Unregistered Guest)]

Joe,
My table is built up with a layer of 3/4" sealed baltic birch as the base for stifness, and then I glued a sheet of 13mm Sintra pvc down as my sacrificial top. I t is pretty stable, and it is not affected by moisture. It wont hurt a tool if you happen to cut into your top, which believe me, I have never done. I put the hurt on it. I cut into it and screw into it. Vac channels cut nicely into also. It has a little static but not bad. I resurface about once a month as needed. It also is not dusty like mdf. Another plus is that is is bright white and its easy to see thru your cut to the table. I pay about $90 per sheet but it is worth it.
Matt

[joe]

Matt,

Very good idea you have with the pvc.

Because of time restraints and the lack of anything better, we've used whats in the shop, .75" Extira.

Our Y carriage is at the local welding shop being perminently stuck together. Although we don't use our SB every day, the fact it's not ready to go is un-nerving.

Joe

[davidallen]

I have the Raptor staples and showed them at a NJ camp several years ago. they work but they are a bit expensive if reusable spring clamps will work.

also after you pull them up, you still need to remove the plastic stems that are left in both the table and the cut pieces.

I think their best application is in resin layups and exposed areas where corrosion and staining are unacceptable.

da