Fly cutting sacrificial sheets

[Dale Wills]

We have ordered in a pack of 6mm MDF to act as our sacrificial sheets. I have been instructed that we don't need to fly cut them initially and that we should only need to fly cut them once there is too many cuts made in them.
Now we are having problems with parts holding when machining. I really feel that this is because we need to fly cut the 6mm MDF before we even start to use them. Once that hard outer surface on each side of the MDF is machined off then we should get much vacuum hold down.

Do you guys fly cut your sacrificial sheets before you use them? And, what thickness sacrificial sheets do you use?

Cheers,

Dale

[Gary Urlacher]

When I got my Thermwood, The tech who set it up got me to fly cut the 1/4" MDF (Both sides)
Then he instucted me to always flip the sheet when I fly cut it. This means that when the sheet
is well used, fly cut it then put that side down. This helps stop any curling of the sheet.

I have been doing this and parts seem to hold well.

Gary Urlacher

[Ryan Hochgesang]

I have also seen that Flycutting both sides of the Handling Sheet, as well as the 3/4" spoilboard is helpful for increasing holddown.

[Nick M Singer]

Ryan do you mean a 3/4" sheet facilitates better hold-down than a 1/4" sheet?

[Ryan Hochgesang]

No. Sorry, I was trying to imply that you can also flycut both sides of the 3/4" spoilboard in which the 1/4" handling sheet is on top of, to get better flow.

[Nick M Singer]

No I am sorry Ryan. Just being thick and not reading properly. Wont do it again!

[Brad McIntosh]

Nick,

Main Spoil Board-
Our experience here in Canada with our customers indicates that a new main spoil board should always be machined on BOTH sides. The surfaces on both sides of the sheet are somewhat "sealed" in the manufacturing process. The surfacing of both sides opens up the fibers and allows a greater flow through the material.

Waste Boards (SPACERs)-
Experience has also lead us to suggesting to our clients that they start off with a SPACER (or waste board) with an initial thickness of 3/8" (9.5-10 mm). 1/4" becomes too flimsy too fast and begins to curl up at the corners. The 3/8" material allows for a couple more "re-surfacings" before the curl effect makes them unusable.

A couple of other notes:

Periodic Re-Surfacing of the Main Spoil Board-
Since the main spoil board does not get machined into on a "regular" basis by your normal production, some of our clients have gone months without "touching up" the top of it by re-sufacing and removing 0.010" (0.254 mm) or so. What these clients also found was that they would start to have the following issues: 1. The efficiency of the hold down would decrease -and- 2. Their depths of cut would become non-uniform.

We recommend that the main spoil board be re-surfaced once a month at a minimum. This levels it out from thickness variations that can be caused by uneven thickness expansion due to humidity changes, etc. The main spoil board also acts as a filter for the fine particules/dust that is constantly being pulled into it - slowly clogging the top surface. Manipulating waste boards (SPACERs) -sliding them on and off, flipping them over, etc - also can close off the porousness of the top surface. The re-surfacing opens up the top surface and can help to reuvinate your vacuum efficiency.

Alternating the "Face-Up" of the Waste Board (SPACER)-
Some of our clients will run X number of sheets with one side of the waste board and then flip it over and run another Y number of sheets before re-machining both sides. Although this does not reduce the amount of re-surfacing, it can extend the continuous working cycle between re-surfacing operations. Another side benefit is that curl that can develop in the waste board is minimized by the uniform machining of both sides towards the core of the sheet. This seems to work well with a waste board (SPACER) that starts off with 3/8" material.

Hope this helps a bit...

* Your results may vary.

[Paul Ford]

Hi Dale,
I used to use 6mm waste board but came across the same problems that you are having. Painting the edges to seal them helped a fair bit. I now use 3mm waste board and don't bother fly cutting or painting. I have been doing it this way for 2 years now and had great results. The only problem you may find is the 3mm can be a little flimsy when sliding it off the machine onto a trolley but you soon get used to it and it works well.

[Dale Wills]

Paul,

How do you go with variance in the thickness of the 3mm? I'm keen to fly cut our sheets now as to intensify the vacuum flow and ensure a level surface. I'm open to suggestions and will give your 3mm idea a test.

Dale

[Michael S Murray]

Ok guys,
Heres a completely different approach and it works for me.
I flycut the spoilboard both sides
I get my spoilboard height set up
I put a 1/4 wasteboard on and flycut it
I pull the wasteboard off and run a small bead of wood glue around the perimeter of the spoilboard.
I put the wasteboard back on surfaced side down, pulling it out to the pop up pins
I throw a 3/4 sheet of anything on top and then turn on the vacuum for about 30 minutes, this pulls the spoilboard and wasteboard down tight.
After the glue is dry I surface the spoilboard and am ready to go for quite a while.
I just take .010 or .015 off the wasteboard when it needs it and when it gets down to .050 or so thick I just flycut the rest off and start again.
This eliminates getting chips between the sheets, elimates the curling edges, eliminates the waste board moving.
Works for me......

[Brad McIntosh]

Mike,

Great way to create a "re-laminat-able" spoil board . That would certainly reduce/eliminate the curl, etc...

Some people might figure on just starting off with a 1" thick sheet of MDF as the main and only spoil board. But your technique reduces the frequency of having to discard the un-machinable 1/2" or so below the tables aluminum edges - and then having to size-to-fit and resurface both sides of a new 1" sheet. (Although that 1/2" spoil board "discard" could possibly be used as the start of a wasteboard sheet... ??)

Most of our clients work with the "unattached" wasteboard as they are looking at unloading the cut parts off the table quickly, loading another sheet and getting the machining cutting while the operator labels and organizes the previously cut set of parts. They would have at least two same-thickness wasteboards to do this - cycling between them. Many will also have a third or fourth in reserve so that they can introduce them in the middle of a job if the cut-through pattern get to dense and the hold-down efficiency drops. Production does not have to be disrupted mid-way through. They will then resurface them all at a convenient time in the production schedule.

If the whole unloading and/or cycling concept is not required, your technique can certainly be a good way to go. Again, great idea.

Cheers,

[Will Williamson]

One thing I would like to add that seams to help a lot is that I cover my spoil board with a roll of pvc when the machine is setting idle (night , weekends)It has helped reduced edge curl and I also use this same roll of material to cover exposed unused areas of the spoil board when cutting to increase vacuum I either roll it up or fold the material to keep it away from the working area This pvc material is pvc sign banner it come in various lenght and widths

[Gary Urlacher]

I was talking to a guy I know that has a couple of Komo machines. He said something interesting and I thought I would
put this out there for feed back.

He said that they were told not to use a waist board. He said that the way to do it is to monitor the vacuum gage.
He said to turn on the vacuum pump without anything on the spoil board and mark down the number (vacuum gage).
Then, add the Melamine or what ever you cut onto the spoil board and mark down that number. He said the differance is the
accual holding vacuum power. He finds that the holding power number increases a lot but not using a waist board.

This makes sense to me yet the thought of the waist board slowing down the CFM also makes sense.

Now I am not sure what to think.

Gary

[Damon Nabors]

I have been following this thread and my question is, are any of you guys finding any 1/4" 5x10 sheets out there to use as waist boards? I was getting 5x8's and splicing them but now I can't even get those. 4x? is the biggest sheet I can get unless I want to buy a skid of them. For me 96 waist boards would go a long way and take up more real estate than I am willing to give up.

[Rob Davis]

Damon,
I hate to admit this but we use 1/4" 5x10 sheets for wasteboards. We use truckloads of 3/4" x 5x10 MDF for products we make and these sheets come as a protective cover from the maufacturer. Guess I am too cheap to buy my own but we take the better ones and flycut them and use them as waste boards. Lots of times they are junk sheets and not able to be saved but because sometimes they are as if they were brand new, that must mean they make the stuff. We pull the good ones, fly cut one side and just skim the other side to break the seal, and keep them for the router. We buy this from Blue Linx (formerly Georgia Pacific). When we heard "waste" board, we figured we could use waste boards.... Haven't bought one in 2 years. Maybe I should start selling these? I am guessing Thermwood does not necessarily recommend this but it works for us. If you need their contacgt info or whatever, email me.

Gary,
We tried once to run without the wasteboard but there is something about the wasteboard that helps make the vacuum more uniform on our machine. Without the waste board, we had trouble with small parts moving and I really hate digging into that low density MDF sheet in the table. Maybe we have the wrong impression but it seems like the wasteboard (in good repair) helps with hodling down at our shop instead of hurts.

Will,
We keep our table covered in melamine or laminate sheets any time we are not using it for humidity and dust. Melamine preferably for weight to keep it from warping.

Rob