What to use for table?

[MArruda]

Hello all,

I'm currently using a CNC that I built off the FLA-100 plans. For those unfamiliar, the FLA-100 is a 24x36" table top out of 8020 extrusion with flat steel ways and roller bearing linear motion. The table frame is unsupported- there's a large open area in the center of the frame that doesn't support the center of the table. Here's my table genesis thus far-

1- First trial was 2 sheets of 3/4" MDF, screwed together with T slots cut into the top surface, milled down to match the Z axis. Worked okay, but the MDF couldn't handle the pull of the clamps in the T track, so redesigned to use actual T track. Also had a slight sag in the center of the table.

2- Second trial, which is currently in use, is a single sheet of 34" MDF. I dadoed 8 channels in the top surface to lay aluminum T slot running along the X axis. I then drilled through the MDF and through bolted from the T track, through the MDF, to 1x1" aluminum tube spanning the table running in the Y axis, parallel to the T track with a lock nut on the underside. The MDF is sandwiched between the two pieces of aluminum- T track and 1x1 tube. This seemed to work well, and took most of the sag out of the center of the table, to the point that I could mill it out with the CNC to zero the Z. From there, I use heavy duty carpet double stick tape to attach strips of 1/4" hardboard to the MDF between the T tracks, to act as the sacrificial top.

The issue I'm having is with the hardboard, and MDF fixtures I clamp to the top, moving after planing. It's fine for a day or two, but after that, the material settles and expands in some areas, giving a variance of up to .020. I'm trying to use this for a production run, so it's not doable to recut the table every day.

I'm using vacuum fixturing as well, made out of corian. They work great, but are flexing to conform to the warpage in the table some what and transfering the inaccuracy to the corian. My problem is that I'm cutting out small pieces of Cocobolo, less than 2 sq in in surface area. I cut it on the vacuum fixture, leaving an onionskin, and then make a final pass to clear the .020 onionskin. As you can guess, with the variance in the table, it's resulting in premature cut- through of the onionskin before the final cutout pass.

My requirements for these pieces is an accuracy and variance of +/- .004. I'm getting that, but not in the Z due to this issue. I think I'm expecting more of a machine made for wood than I should, but I am getting it for the most part; it seems people using MDF as a spoil board don't need this kind of accuracy.

Here's my thinking for a good, solid, flat table-
3/8 or 1/2" aluminum sheet, bolted to the frame. Then, a 1/2" piece of Corian screwed to that, with dadoes cut for aluminum t track. From there, I'd surface the corian and it should be good, with little to no expansion and contraction in the Z axis, thus aleviating my problem. I could just use a piece of aluminum, but I would like to have the corian as a spoil board. I could use UHMW or something like that, but I'm concerned about the low drag coefficient leading to workpiece movement.

I'm in the high desert of Ca, temps averaging 100 degrees this summer, 0-20% humidity. I work in a climate controlled shop.

Thank you for your input and sorry for the long windedness,
-Michael

[MechanoMan]

I came here for a similar question on a 4x8 router bed. Well, it'll need to be able to hold down 4x8 sheets of MDF, which are actually 49"x97" plus a margin for the clamps. So, a bit more.

My initial thought was to countersink bolts into 3/4" MDF, bolt the MDF down, surface, and drill a bunch of holes that miss the 8020 work support members.

But that would require installing T-nuts or bolts under the table most of the time I need to change the work solution; almost a 2-man job there.

If I was gonna do T-slot, would I have to glue together 2 sheets? Is gluing difficult? What's the recommended dimensions for T-slot in MDF?

What about Corian? Is it worth the price?

[louieatienza]

You could also use a paper-based phenolic; there are a few commercial CNC makers that have it as an option for their table beds. Durable, stiff, heavy, and probably cheaper than a similar piece of aluminum. Probably better vibration damping than aluminium. You could then surface it and add your spoilboard/t-tracks as well... Also you won't kill your bit if you run into it.....

[zool]

Look at this site for paper-based phenolic: Phenolic high pressure laminates, carbon fiber & laminated plastics - Current Inc.

Look at my build for how I hope to solved sagging table top problems with closely spaced aluminum cross pieces; see especially entries 1, 26 and 27: http://www.cnczone.com/forums/cnc_wo...ized%5D-3.html

I am contemplating not using a table at all, but using a variety of sizes of vacuum pods and large rectangular vacuum chucks. I have seen a number of high-end high-speed production CNC routers that do not have a table, just vacuum pods. You can see them in this video: ‪Breakfast Woodworks CNC machines Hauer Ceiling piece, quartered white oak.‬‏ - YouTube
The five-axis CNC router in the above video is about 1/4 mile from Long Island Sound. No air conditioning in the studio as the studio is about 5,000 square feet in an older mill-style industrial building [more holes than Swiss cheese!].

My studio is 1/2-mile from Long Island Sound, and humidity in summer runs 80 to 100-percent with temperatures 75 to 100-degrees Fahrenheit at midday. No air conditioning [even though it is a two-year old building]. The overhead door and entry door both face west with a scenic view of a black topped parking lot and another metal building across the parking lot. I am there from 7:00 AM or so until twelve-noon or so and come back around 8:00 PM for a couple hours. Both my CNC routers are there all the time and thier steel parts, and the cast iron table tops on the other woodworking tools, get waxed a lot, though still show rust, as do my planes and other hand tools on occasion no matter how much I wax them.

Louis knows all about working in damp places as he works in a dank subterranean space with large spiders. Supposedly he makes nice guitars, but I gotta wonder what he is REALLY doing down there!

[zool]

Vacuum Pods Better Vacuum Cups, Inc

‪RoboCNC Router : Vacuum work holding‬‏ - YouTube

Here is a really cool way to make a vacuum pump. Project: EVS - The Concept

[louieatienza]

Originally Posted by zool Look at this site for paper-based phenolic: Phenolic high pressure laminates, carbon fiber & laminated plastics - Current Inc. Look at my build for how I hope to solved sagging table top problems with closely spaced aluminum cross pieces; see especially entries 1, 26 and 27: http://www.cnczone.com/forums/cnc_wo...ized%5D-3.html I am contemplating not using a table at all, but using a variety of sizes of vacuum pods and large rectangular vacuum chucks. I have seen a number of high-end high-speed production CNC routers that do not have a table, just vacuum pods. You can see them in this video: ‪Breakfast Woodworks CNC machines Hauer Ceiling piece, quartered white oak.‬‏ - YouTube The five-axis CNC router in the above video is about 1/4 mile from Long Island Sound. No air conditioning in the studio as the studio is about 5,000 square feet in an older mill-style industrial building [more holes than Swiss cheese!]. My studio is 1/2-mile from Long Island Sound, and humidity in summer runs 80 to 100-percent with temperatures 75 to 100-degrees Fahrenheit at midday. No air conditioning [even though it is a two-year old building]. The overhead door and entry door both face west with a scenic view of a black topped parking lot and another metal building across the parking lot. I am there from 7:00 AM or so until twelve-noon or so and come back around 8:00 PM for a couple hours. Both my CNC routers are there all the time and thier steel parts, and the cast iron table tops on the other woodworking tools, get waxed a lot, though still show rust, as do my planes and other hand tools on occasion no matter how much I wax them. Louis knows all about working in damp places as he works in a dank subterranean space with large spiders. Supposedly he makes nice guitars, but I gotta wonder what he is REALLY doing down there!

I've been very fortunate that although my dungeon is a big dark, it has stayed relatively dry, despite having 100 year old stone foundation walls. But when I'm not formulating my palns for world domination, I DO build guiats, custom furniture and woodworking, signage, and other various oddities...

If you're in the NY/NJ/CT area I have a supplier of phenolic at a good price; I've bought 4 x 8 x 1" for a few commercial projects.

[stevespo]

I'm with zool on this one. Why not install some 8020 cross pieces to support the MDF sufficiently?

My work area is 25x36", with (3) 1530 supports on about 8" centers. I use a single sheet of 3/4" MDF attached to the t-slots for my "worktable". I surface it when it's showing a lot of wear and tear, but it stays flat and stable. Some phenolic coated baltic birch or other high quality ply would also work nicely.

I like the fact I can easily drill indexing holes for vacuum fixtures, nail or screw parts down, or use double stick tape. Lately I've started using a second piece of MDF (true spoil board) on top so avoid wear and tear on my reference surface.

I've considered using a 1/2" thick piece of Mic-6 AL plate, and possibly incorporating some type of t-track, but I really like the options with the MDF. Plus when you accidentally plunge a spinning bit into it, you can patch it or easily replace it.

Corian might make a stable table surface, but I wouldn't use it for a spoil board. Stick with MDF, and add aluminum supports underneath. Even with a 1/2" piece of cast AL plate, I suspect it would sag some amount and cause problems without the supports.

Steve

[MechanoMan]

Originally Posted by stevespo I'm with zool on this one. Why not install some 8020 cross pieces to support the MDF sufficiently? My work area is 25x36", with (3) 1530 supports on about 8" centers. I use a single sheet of 3/4" MDF attached to the t-slots for my "worktable". I surface it when it's showing a lot of wear and tear, but it stays flat and stable. Some phenolic coated baltic birch or other high quality ply would also work nicely. I like the fact I can easily drill indexing holes for vacuum fixtures, nail or screw parts down, or use double stick tape. Lately I've started using a second piece of MDF (true spoil board) on top so avoid wear and tear on my reference surface. I've considered using a 1/2" thick piece of Mic-6 AL plate, and possibly incorporating some type of t-track, but I really like the options with the MDF. Plus when you accidentally plunge a spinning bit into it, you can patch it or easily replace it. Corian might make a stable table surface, but I wouldn't use it for a spoil board. Stick with MDF, and add aluminum supports underneath. Even with a 1/2" piece of cast AL plate, I suspect it would sag some amount and cause problems without the supports. Steve

For me, I'm not looking to use the work surface as spoil, nor am I trying to substitute the 8020 work support crossmembers with a stronger work surface- 8020 work support is already a given.

What I was looking for is a work surface with superior work holddown solutions. The question was, is MDF really a durable thing to T-slot? Also, there is a possible case where I'd be grinding fiberglass with water coolant, and water-based coolant and MDF don't mix AFAIK.

[zool]

MechanoMan stated: What I was looking for is a work surface with superior work hold down solutions. The question was, is MDF really a durable thing to T-slot? Also, there is a possible case where I'd be grinding fiberglass with water coolant, and water-based coolant and MDF don't mix AFAIK.

You can put t-nuts in the bottom of the MDF as the nuts to the screws/bolts to secure the t-track.

There is an exterior type of MDF you might look into if you are going to be using moisture when cutting. Though the phenolic might be a better bet if you are faced with moisture in your machining operations..

You might try misting the fiberglass rather than flooding it when you cut. Use a two-stage dust collector to vacuum up the minimal amount of moisture and the nasty ole fiberglass swarf. For the collector, use a plastic trash can with a plastic cover, this will keep the fiberglass swarf and moisture out of the dust collector itself. Look at this you tube video .. not the best video, but the idea and execution is very good.

‪2 Stage Dust Collector‬‏ - YouTube

‪2 Stage Dust Collector‬‏ - YouTube

[stevespo]

Ah, I got it. I didn't understand you were already doing the 8020 supports. Yes, the MDF and coolant don't work well together. I've used some custom corian and HDPE fixtures with a built in tray to hold water and allow misting, but you have to protect the MDF with 4mil plastic. Not ideal.

There are some water-resistant products that people have recommended, but I have not tried them. Extira is one brand name. When I looked into it I believe it was fairly stable dimensionally, but not completely.

Some friends have been using a product called PaperStone, which they get as remnants from the counter top fabricators. It's like a paper-based Micarta (phenolic based) and machines nicely and appears to be very stable. Comes up to 1.25" thick and doesn't cost a fortune as off-cuts. I suspect you could easily dado and epoxy in some aluminum t-track, even tapping holes for bolts.

A piece of 1/2" Mic-6 AL is not that expensive for a benchtop machine, so that is another option. Would make a nice work surface with index and tapped holes on a grid, with the option to screw down any number of fixtures, including t-slots.

Steve

[MechanoMan]

Originally Posted by zool MechanoMan stated: What I was looking for is a work surface with superior work hold down solutions. The question was, is MDF really a durable thing to T-slot? Also, there is a possible case where I'd be grinding fiberglass with water coolant, and water-based coolant and MDF don't mix AFAIK. You can put t-nuts in the bottom of the MDF as the nuts to the screws/bolts to secure the t-track. There is an exterior type of MDF you might look into if you are going to be using moisture when cutting. Though the phenolic might be a better bet if you are faced with moisture in your machining operations.. You might try misting the fiberglass rather than flooding it when you cut. Use a two-stage dust collector to vacuum up the minimal amount of moisture and the nasty ole fiberglass swarf. For the collector, use a plastic trash can with a plastic cover, this will keep the fiberglass swarf and moisture out of the dust collector itself. Look at this you tube video .. not the best video, but the idea and execution is very good. ‪2 Stage Dust Collector‬‏ - YouTube

I'm very concerned about the cost of mounted metal T-slot on a 4x8 bed. The T-nuts, as I said, are an "idea", but I'd be going underneath the table to move them pretty frequently. The cost of filling the entire thing with fixed T-nuts could be cost and time-prohibitive. Mounted 2" apart, I'd need 1152 of them. I suppose they're cheap enough that I could place them "as needed" and never move them, just keep adding more. Still, I feel I'd be under that table quite often. And the fact remains that the spacing between nuts would be wide and not variable to snug up to the work.

Also I'm not familiar with these other products, price and where to get in large sizes locally. MDF, I saw I can get that cheap enough, like $25 a sheet. If it's not local, then shipping cost may well be quite excessive.

I tried misting the fiberglass, it was one of the worst options because the fiberglass tended to turn to sticky mud rather than flowing off the diamond grinder. Oddly enough, it seems like a solid stream actually spatters LESS.

[zool]

MechanoMan stated: What I was looking for is a work surface with superior work hold down solutions. The question was, is MDF really a durable thing to T-slot?

As MDF is wood fibers mixed with glue which is then compressed to make the material, it had little or no structural characteristic, hence is not an appropriate material to t-slot for secure hold downs which can be trusted for realistically exact repeatability..

Given what you have explained, putting aluminum t-track in the MDF, with metal backing on the bottom side so bolts do not pull through would be the best course for you.

Another idea would be to use aluminum or phenolic for the table, attached the aluminum t-slot to that and then use MDF as a spoil board, fitting it between the aluminum t-track.

The latter be more expensive, but would be easier to replace the MDF than in the case of just using one layer of MDF.

But given your aversion, with which we all agree, of climbing underneath your machine, the latter choice would seen the best.

The only draw back to the latter choice is that "stuff" will no doubt start to accumulate and multiply .. but that is another issue with which we all wrestle, sometimes literally, though mostly figuratively as we just ignore it!