Spoil board

[3d_danny]

I am putting the last coat of paint on my "shorty" alpha table. http://www.talkshopbot.com/forum/messages/7/7398.html?1113756737
I hate painting metal.....

I am ready to buy the wood for the table top and spoilboard. The ShopBot table I saw at the jamboree had a spoilboard that extended past the cutting area of the machne so when it was surfaced, it created a pocket in the spoilboard. It would seem to me that with a pocket, the material to be cut would be limited to the size of the pocket. Would it be reasonable to assume that the spoilboard should be the same size as the cutting area so a large piece of material would still lay flat?

What size is best for the table top as well as the spoilboard and what is the best way for attaching the spoillboard?


Dan

[Brady Watson]

Dan,
Not sure what you saw @ the Jamboree...but that is not typical. Most of us use the CR command with pocketing routine to surface the spoilboard...but I have never heard/seen of anyone leaving a pocket in the center of the spoilboard (unless it was a vac hole).

As far as spoilboard material goes, birch plywood is popular on 4' wide machines, and Medex is what I use for my 5' wide machine because I cannot get 5X8' ply that is suitable for a spoilboard. I like the Medex much more than MDF because it is more stable, less susceptible to the effects moisture, and doesn't (supposedly) have formaldehyde in it.

-Brady

[3d_danny]

Brady,

If I understand you correctly, the spoilboard is the same size as your cutting area?

Do you use the Medex for both the support board as well as the spoilboard?

How do you fasten the spoilboard to the support board?

[fleinbach]

Dan

I used a 1" MDF support board and spoil board. I attached the support board with 1/4" carriage bolts using the shopbot to counter sink the heads. Then I did the same with the 1" spoil board. But used screws to hold it to the support board counter sunk 5/8" so I could resurface several times.

It was usless for me to worry about the formaldihyde since I cut 95% MDF anyway.

[mikejohn]

Dan
What I have just done is this. My spoil board was cut about 25mm oversize all round.
Find the four corner positions where the pinions are about 2mm from the stops.
CR the table with as wide a bit as possible (25mm in my case). Then change the bit for a 6mm (1/4") bit. Now cut around the perimeter, going as close to the stops as you feel comfortabe with (I stuck to 2mm), and as deep as you feel necessary (don't hit the cross members)
. Remove the waste outside of this cut line. Your table is now flat all over your cutting area, with no lip. With a 3mm (1/8") bit you could cut 1.5mm (1/16") outside of this cutting area, but I think you can live with that.

By the way, where in physics does is say that the amount of dust this creates is 10 times more than could posibly have been in the 1mm of material you removed?
............Mike

[gerald_d]

Dan, our boards are wider than the cutting area in the y-direction by about 30mm per side and longer than the extreme x-cutpoint by about 50mm. So, we often have a ridge sticking up proud of the surfaced spoilboard. The ridges make a great reference edge. On the very rare occasions that we have to work with material that is larger than the cutting area, we lay a spacer sheet underneath. Sometimes a new spoilboard, glued in only the "surface-able" area, rises out above those ridges, and then we miss our reference edges. We also have heavy bolts pulling these "ridges" down onto the cross-members, and we know our cutter can't ever hit those bolt heads. But I wouldn't be so presumptious to say this is the right way and that a narrower table is the wrong way - there are pro's and con's for each.

[gerald_d]

3156

The green bit is a 6mm cutter running close to the stop - similar to Mike. White is the "support" board of 25mm MDF. The red on the right is the first "spoil" board, also 25mm MDF. The left side reds are later spoilboards, glued to the lower boards - explained in this (http://www.talkshopbot.com/forum/cgi-bin/discus/show.cgi?tpc=7&post=15420#POST15420) post. (Hope that the dimensions in that post correspond to those in this post
)

The long bolts through the edge were a later addition - we found that we needed a stronger edge because of all the g-glamping that happens along that edge. (we had pulled our support board away from the blue cross-members in silly attempts to pull warped wood down flat.)

[stickman]

Hello everyone,

I just got done replacing my spoilboard. I used 3/4" melamine before and thought I was happy with that, until I put this new one on. I used MDF and quite suprised at the difference. The melamine / particleboard was just different, in the fact th melamine was alway sharp on the edges and I was beginning to find that it didn't keep the screws the best. With the MDF top I added about 12 more screws, but that was in light of the findings that I had when I pulled the spoilboard up. In many places the melamine / particleboard had pulled up for months of machining and removing material. It was contracting and cupping.

Anyhow, just another note on top removal. I zeroed the bit to the table surface and then had it cut the spoilboard into squares, missing the screws of course and not cutting into the support top. That worked really good, it allowed me to easily handle it off the table.

[slendon]

Had screwed my MDF spoilboard to the table from underneath, whilst cleaning under the table found several screws on the floor......looked up and realised they were those that had worked loose and fallen out!! most of the others were loose too. Checking from above showed that my spoil board was indeed not tight to the table.

The next board will be glued down (as per Gerald)

Have a quick look at your spoilboard!
Steve

Is the moral of this to clean up more often, or do the job right first time?

[gerald_d]

Steve, those screws saw a cutter approaching, so they ducked! These are very special intelligient screws, sold on the east of the Atlantic only.

[slendon]

Gerald, Found the end user agreement that came with the screws which states that the intelli screws work in direct proportion to the intelligence of the end user,...... mine took 16 months to work out when to duck!

[gerald_d]

That's why they stopped selling on the west of the Atlantic - there they never learnt when to duck.

(Hey, any feedback from your son? I am sure that he is doing fine!)

[mikejohn]

Today I surfaced my spoil board. It needed doing as it resembled the surface of the moon.
As it was working away, I felt there was some problem. I was cutting 1mm (0.04") deep. I was getting some ridging at either end of the table, and will shim to correct this,but something else felt 'not right'. It sounded wrong in places.
My table top is attached as Geralds picture above (http://www.talkshopbot.com/forum/cgi-bin/discus/show.cgi?tpc=7&post=24108#POST24108) with the spoil board glued on.
Roxana came along to find out what I was chuntering about, decided to have a look, and found all the nuts loose that hold the table to the crossmembers.

Some of these I could tighten 1 to nearly 2 turns, which is a distance of 1 to 2mm with the bolts I am using.
What is the best thing to do to stop this repeating?
Anyone else had the same problem?
.................Mike

[gerald_d]

Not had the same problem, but there are a number of classic ways to stop nuts from working loose.......

- Make sure it has been properly tightened. If the clamped material tends to settle, then re-tighten after the settling period.
- Drill and lockwire the assembly ala aircraft style. An overkill for a SB
- Use one of the scores of types of "lock-washers"
- Use Loctite
- Use Nylock nuts

I would go for the re-tightening only. If the nuts still work loose after that, I'd try Nylocks.

[mikejohn]

I guess it one of those thing that, having happened once you keep a much closer eye on it in the future.

..............Mike

[wemme]

Hello
I have an MDF spoil board laying on a leveled bed of support rails in both x and y directions. the spoil board has a habbit of currling due to moisture content. would a sheet of marine ply be a better choice? has anyone else had similar issues?

[kerrazy]

are you using a sheet of Cabinet grade ply first attached to your rails? If so I would suggest using Extirra MDF as a spoilboard, as it does not accept moisture so easily.

Dale