Let's Talk About Table Flatness

[Burkhardt]

Gert - I'd love to get away with 3/8" hose and couplings, but the plumbing has to be sized for the pump CFM. In my case about 200 CFM, where 2" is what the engineering charts point to for free air flow. ...

-B

Wow, that is a lot of volume for pods and the skinny hose surely won't do. In my case I have only a high vacuum GAST pump that does maybe 4 cfm but I have used it successfully for custom shaped pods up to 15" x 20" or maybe double that size when 2 pumps are used.

I have modified my 36"x48" 80/20 table (consisting of 3-slot 4515 extrusions) that a few of the middle slots are closed (thin aluminum flashing taped on) and act as the vacuum conduit. I can punch a hole anywhere along the slot and only need a re-usable non-stick gasket (cut from foam-type drawer liner) to hold down a board for one-sided work, no real "pod" needed. I even hold down the indexer and tailstock or the machine vise that way when used. But that would not work as well for your high volume vac system.

When using any aluminum table on a steel frame, keep in mind the thermal expansion of aluminum is twice the expansion of steel and for an 8' long machine that can become substantial. It can be 10-15/1000" difference for a 20 deg F change which does not sound much but could bow the table when not allowed to move relative to each other (e.g. mounted on standoffs).

[Brady Watson]

Just a thought,you have a lot of wood products right now, (base, plenum, spoil) that's a lot room for movement. Instead of using 8020, why not use a sheet of 3/4" 6061 Aluminum plate? With the 8020 you have a lot of smaller pieces that have to be aligned and secured to each other or they can move independent of each other. A sheet of 6061 weighs around 514 lbs. A bit heaver than 8020, yes, but a lot more stable. A few extra cross members will handle the weight. A heaver machine is a more stable machine. The expansion coefficient is minimal. You could machine your grid right in to it and use gasketing or use a structural bonder and attach another plenum board.
With regards to the MDF shrinking, could it be with a 13 hour run, the moisture content is going down in the board with that much air flow going through it? That time of the year, dry, dry,dry. With the big guys running heavy iron, there changing there spoil boards so frequently they don't have a problem with it shrinking.
Double refined MDF. Try Ranger Board by West Fraser. Awesome product, finishes out after machining like it has been sanded to 150. Also no extra edge sealing, the edges absorb the same as the flats.

I was considering sheet AL (probably 1/2" is more than adequate, but $900/sheet @ 4x8' x 3 = $2700) and phenolic sheet as well; but to cover a 5x16' area they're both more expensive and have less utility than the 8020, because both lack t-slots. I'd like to bump up to the 1.5" stuff (1530/1545), but that brings the grand total closer to $4k for the job. Plus, a 1/2" or AL sheet is cumbersome to handle even with a front loader and cherry picker. It would also be dicey putting MDF on top for a bleeder...

Initial testing of a piece of 1030 shows that it's pretty darn stout between the crossmembers and I'll never put enough weight on it to have it deflect any measurable amount. I don't think expansion and contraction is going to be much of an issue. There's still no getting around doing a flattening routine to get things flat to the gantry/spindle from time to time. If I sense that things are too up or down, bolts holding the substrate to the 8020 can be loosened to allow it to relax and then tightened down again. As I said, the DT tool has proven to be excellent for flatness...granted this is a much larger area, but I think it's way better than relying on wood with temp/humidity swings.

I'm leaning towards replacing the 2x2x1/4" angle iron crossmembers with 2x3x1/4" wall steel tubing...It will provide twice the support and deflection resistance according to deflection calculations.

Yes, it's a lot of work getting them properly secured, aligned and flat - BUT - I only have to do it once. Plus, I have robots to drill holes for me exactly where I want them. There's only going to be about 860 of them by my calculation...

Thanks for the tip on the Ranger Board - I'll check it out.

Wow, that is a lot of volume for pods and the skinny hose surely won't do. In my case I have only a high vacuum GAST pump that does maybe 4 cfm but I have used it successfully for custom shaped pods up to 15" x 20" or maybe double that size when 2 pumps are used.

I have modified my 36"x48" 80/20 table (consisting of 3-slot 4515 extrusions) that a few of the middle slots are closed (thin aluminum flashing taped on) and act as the vacuum conduit. I can punch a hole anywhere along the slot and only need a re-usable non-stick gasket (cut from foam-type drawer liner) to hold down a board for one-sided work, no real "pod" needed. I even hold down the indexer and tailstock or the machine vise that way when used. But that would not work as well for your high volume vac system.

When using any aluminum table on a steel frame, keep in mind the thermal expansion of aluminum is twice the expansion of steel and for an 8' long machine that can become substantial. It can be 10-15/1000" difference for a 20 deg F change which does not sound much but could bow the table when not allowed to move relative to each other (e.g. mounted on standoffs).

Gert,
I also have a couple of little Gast pumps and use the smaller tubing with them. I learned early on to err on the side of bigger is better when it comes to vac tubing because I remember not being able to make a seal even with an 11-gal surge tank because the tubing was too small...'like sucking through a straw' - quite literally! It certainly did cross my mind to exploit the internal cavities of the extrusions for vac plumbing...but aside from needing multiple feeds to make up for the smaller equivalent tubing diameter, there was also the issue of sealing both ends of the extrusions air tight. That means drill/tap/gasket and bolt at least 40 caps...I think for me, on-board PVC pods etc with them bolted to the 8020 would be fine. In fact, it is very rare for me to use the small vacs on the big machine because the bigger vacs are available right there.

Most of the time I'll just make a 'direct air' pod, puck or fixture out of whatever scrap I have laying around. I made one last week, printed out an adapter and plugged in some 1.5" corrugated hose...The hose held up under 25 Hg" - so I am considering using some of it for the 'quick release' setup when I want to remove the vacuum grids and just machine on the 8020. I reverse engineered a push to connect fitting and scaled it up to fit a 2" PVC pipe...the problem is that it doesn't scale well - looks goofy(!) - and while it seemed like a good idea on paper, it's too wonky to use in real life. Then I was thinking about something more compact - why not a compression fitting?...then again, why not just plug a 2-2.5" ShopVac hose in or out of the zone and be done with it?! So I am thinking in this direction now. They have nice hose end fittings/cuffs for the corrugated pool/car wash hose, it won't crush down and leakage doesn't seem to be a problem. I'd just adapt from the existing PVC manifold or run to a flex hose and be able to plug/unplug as needed.

In terms of expansion/contraction - I'm going to see how it goes. My initial thought is to slot the thru holes to both deal with the possibility of piece to piece stack up errors and possibly give the material a place to go if it does expand. This is a tightrope between getting the proper torque to hold things down and allowing it to move. I can't say with any certainty that the MDO doesn't buckle/bow under weather changes - because I just don't have the instrumentation to pick that up. I will say, visually I can't tell - even with a straight edge and dial indicator. Last week for the heck of it, the shop was around 70F and I pre-loaded the dial indicator against the spoilboard. When I came in the next morning there was zero change on the indicator at 46F. Not very scientific, and kind of a novelty test, but I was expecting a change of at least .005".

Attached are pics of the reverse engineered push to connect and how HUGE it got (like 4.5" OD) - and a jig I slapped together last week out of 3/4 & 1/4" MDF - no gasket required. The hose feeds in from the bottom off the table. To secure the jig to the machine, I just put like 10 dollups of wood glue behind the jig to the spoilboard and weighted it down. It came off pretty easily when done...but did take a few pocks of material with it when I pried it up.

More later...

-B

[gundog]

For my clamping portion of my table I bought some extrusion from Hubbard CNC they sell on Ebay. If I had it to do again I would make my own clamping table from 1/2" x 4" 6061 bar stock by just cutting a rabbit out of the corner and placing them spaced so they make a T slot when installed. My extrusion fit 5/16" bolts if I were to make my own I would make it fit a 5/8" slot that way you can buy ready made clamping kits for milling machines.

[bleeth]

Hundreds of things are properly called mills besides a metal working tool, starting with those places that grind grain into flour. Other than that we're pretty much peeing on the same tree as per usual! Getting what you do out of your tools is based on your extreme attention to detail, regular maintenance, and creative thinking. That isn't the norm out there. Like you, I've walked into shops where the owners had told me their machine was no good and in reality the issue was poor set-up and operation.
By the same token, the average user cranking out cabinet parts or v-carved craft signs isn't going to need the absolutely perfect bed either.
Sharing the knowledge for those few fanatics that do want or need to go the extra mile for absolute optimal results though, is always a good thing. Maybe a bit of it will seep down where it will help others as well!

[mporter88]

Hello.
May be my first post here. Lurker/learner forever though.
Have a question and think this maybe a reasonable place to ask it.
Any input appreciated.

I have a 24 x 48 Buddy standard with the HSD.
Love the machine.
Bot at home...Fadals at work.

Now taking a leap into a small personal production run of something I developed on the buddy.
Will purchase a longer stick so I can run 48 x 48
Will also build a 48 x 48 bradyvac with 2 Feins.

If one of you were going to do that..today..what would you do for a base to use all of that new powerstick?
I can give up some Z as I only ever cut panels....so i've thought about a box even.

I am simply routing 1/4inch (6.5mm) melamine board into parts with .125 carbide endmills...and want to get Z cut depth as consistent across the field as I can.

The product would benefit from equivalent depth in all pockets....so want to plan the new setup to FOCUS on that.

Would the Buddy support moving a slab of Aluminum?
Would it kill the steppers?

How about a glue up of Formica..flattened?
Would probably weigh almost as much.
Money is an object for me...but still curious as to best option.

Current base on the 24 x 48 setup (will be replaced) is 1 inch high quality subfloor ply.

Any input appreciated.

[bobmoore]

my vacuum system has been much more stable since I made my plenum out of corian. I have 2 5 horse becker pumps that can be run solo or n tandem with a combined volume of about 175 cfm at 25 inches of mercury. I don't recall the numbers but the corian had less expansion / contraction than aluminum. keep in mind that when you surface your spoilboard the vacuum is severely reduced (especially with a high vacuum pump) compared to when you put a sheet on to cut and cover all of that open spoilboard. We would get some bowing (I seem to remember about .018-.020 inches) even on the Komo vr 510s toward the center of the spoilboard. Bob

[khaos]

Great thread!

BLUF: I primarily do 3D work. I only share here for the lurkers and not to provide a solution for Brady's application.

---

I have to go through spoilboard at a decent clip. I have a 0.75" marine plywood base flattened and then I glue spoilboard on top. Short of going the route of extrusions Brady is leaning towards I can't see much improvement. My PRS 8'x4' lives in my non-heated/cooled shop literally 25' or less from the Nansmond River. Humidity varies from %20 to %80 within a few hours and approaches %100 often enough to mention. Heat swings normally about 20 degrees. So before I work I have to skim the table to remove the hills and dales less the shire attract hobbits. :/

I have an .75 extruded PVC 2'x4' vacum puck/pad that I screw down on the corners. This worked great for smaller and faster cuts (< 3 hours) but longer cuts > 12 hours would result in a wall of shame entry. From the results there is usually a very noticeable ridge in the work. I brush my racks and pinions regularly.

I made an 8'x8" puck for some custom molding and some flooring inlays out of a piece of TREX and that was a great piece of tooling those cuts were usually < 3 hours so it only bears mention because it was unaffected by humidity. The flooring inlays are sensitive to depth of cut as I use straight bits vs the vcarve method. I would skim a 64th or a 32nd off at the planer to finished the work up usually to compensate for some variance in the laminate thickness I cut on my bandsaw.

The best results for me personally have been using a high end subfloor that has a waxy feel throughout. I understand that my results are compounded by all the materials in the cut including and sometimes primarily the working material

I am not a production shop . And Vacum is the rarest form of hold down I use. Screws, bolts and job specific jigs are my lot.

[gundog]

This is how I would make my own clamping table this is an end view.

[Brady Watson]

Mike,
I certainly did consider doing exactly what you show. The problem is, 1/2" AL 6061 would actually cost a little less than the 8020 but still have to be machined, drilled and the steel drilled to accept all those pieces. It's definitely a great idea, but I think the 8020 is the way to go for my setup.

Saw the Hubbard stuff as well as the Techno stuff and other offerings on Ebay et al. All the 20mm stuff seemed too flimsy and I think they can only take a 5mm fastener - so that rules that out. I think 1/4-20 is the smallest I'd want to go.

I'm looking forward to popping my Kurt or Grizzly milling vices on the table. I'll have to make an adapter plate for quick registration, but it's great to be able to really crank down on the metal stuff when machining...Plus align it with an indicator and life is good. I had one on the DT machine when doing some cutting on an awkward to hold aluminum casting.

Got me thinking now Mike...I'm going to have to crunch numbers again and see if AL bar would really make sense for my work...

-B

[waynelocke]

I remade my table plenum last year with 4 2' X 4' X 3/4" pieces of HDPE. I used four pieces so I didn't have to deal with expansion over the whole 4 X 8. This replaced a mdf plenum and the original hassle of sealing it still leaves a bad taste and then even after sealing it it was still barely sufficient compared to the plastic. The top cost, I think about $200.

I know that some have criticized hope as plenum over the years but, although I don't remember the numbers, the expansion over a 20deg temperature change was not bad and was accounted for by drilling larger mounting hole towards the positive x and y directions. The plenum is much more efficient and to this point the table has stayed fairly flat. My shop is air conditioned and heated so there is rarely a large temperature change.