Good material for spoil board?

Good material for spoil board?

Postby Olle » Wed Jan 11, 2017 6:02 pm

I'm cutting a lot of 2-sided parts, and I have made a custom spoil board with studs to make it easy to flip the pieces accurately. However, I have noticed that the alignment gets out of whack now and then, and I think I have it tracked it down to movement in the spoil board. I measured the stud spacing this morning, and it was 3.995" where it should have been 4.000". It's not a huge discrepancy, but the error builds up across the table and it's enough to throw the alignment off. This means that I have to do a lot of sanding to make the parts mate properly, so I want to find a good material for the spoil board.

I'm using 3/4" medium density fiberboard right now, but I figure I would need something synthetic that doesn't shrink or swell with changes in humidity and temperature. There's all kinds of expensive materials out there, but going with something too exotic would make it cost prohibitive. Does anybody have any tips on what to use?
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Re: Good material for spoil board?

Postby Leo » Wed Jan 11, 2017 6:17 pm

Construction lumber (studs) is not a good choice. That wood is what you get from a tree after all the good trim boards are cut off the tree. Also, the trees are fast growth trees with lots of stresses. They also don't get a really good kiln dry. I would stay away from construction grade lumber as it's just not stable enough for what we want.

MDF is much better as it is a lot more stable and relatively inexpensive.

To go better than MDF you will need the more expensive stuff.
HDPE sheet is more stable but VERY expensive and frankly I have never heard of it being.

An aluminum TEE slot table is a good choice. That is what I have and I use 1/4 thick pressed board strips as a sacrificial barrier.
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Re: Good material for spoil board?

Postby dwilli9013 » Wed Jan 11, 2017 6:23 pm

An aluminum TEE slot table is a good choice. That is what I have and I use 1/4 thick pressed board strips as a sacrificial barrier.[/quote]

Any chance you might post a pic of your setup for the pressed strips Leo? Sounds intriguing.
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Re: Good material for spoil board?

Postby gordread » Wed Jan 11, 2017 7:14 pm

Hi Olle,

I have an aluminum t slot track on my table, but for job specific set boards, which it sounds to me like you are using, I use 3/4" MDF.

Fortunately I live in Alberta, Canada, and the humidity is always low, so that doesn't affect my set ups. (and I have a temperature controlled shop, as woodworking in -40' is not an option for me. :)

If you want to ensure that humidity is not a problem with you MDF, then I suggest trying to use a penetrating sealer. I've never done it, but we all put a sanding sealer, or finish on our final projects to avoid humidity issues, so by extension, why not here? And it's got to be cheaper than using HDPE or some other high tech material.

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Re: Good material for spoil board?

Postby Rcnewcomb » Wed Jan 11, 2017 8:33 pm

If you aren't using vacuum then sealing is a good choice to minimize changes due to moisture. Sanding sealer, shellac, basically anything that creates a moisture barrier will help.
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Re: Good material for spoil board?

Postby Olle » Wed Jan 11, 2017 10:03 pm

Leo wrote:Construction lumber (studs) is not a good choice. That wood is what you get from a tree after all the good trim boards are cut off the tree. Also, the trees are fast growth trees with lots of stresses. They also don't get a really good kiln dry. I would stay away from construction grade lumber as it's just not stable enough for what we want.

MDF is much better as it is a lot more stable and relatively inexpensive.

To go better than MDF you will need the more expensive stuff.
HDPE sheet is more stable but VERY expensive and frankly I have never heard of it being.

An aluminum TEE slot table is a good choice. That is what I have and I use 1/4 thick pressed board strips as a sacrificial barrier.

It's not 2x4 studs or anything like that, it's 3/8" ground O1 steel studs :)

I have the 3/4" MDF (actually something more like HDF) pinned and bolted to the T-tracks in the table so it can't move, and the steel studs come through the MDF in a grid pattern. I drill the blanks with a drill bit that's only 2/1000" larger than the studs, and I do it in my milling machine to get the spacing dead on. The studs have threaded ends, so I can use nuts to tighten the blanks down with nuts. The fit to the table should be within a few thousands of an inch, so the whole mounting system is as accurate and free of slop as it can be. The only problem is that the board appears to shrink a swell, which in turn throws off the accuracy of the whole setup.

Sealing sounds like the obvious solution (which I often overlook...), so that what I need to try before I do anything else. I guess I would have to re-seal it now and then to keep up with the boo-boos, but it would be easy to just slap it on as the battle scars occur.
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Re: Good material for spoil board?

Postby Leo » Thu Jan 12, 2017 3:23 am

You have AISI-O1 tool steel studs? You are seeing movement in THAT?

What do you mean by studs? Like 3/8 diameter threaded studs that are parallel to the "Z" axis?

I am confused.

Can you post pictures?

OK - now I read you last post.

Can you post pics of your setup?
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Re: Good material for spoil board?

Postby gordread » Thu Jan 12, 2017 4:42 pm

Hey Olle,

If I understand your situation you have an MDF spoil board into which you insert some steel studs (like dowels from your explanations.) to which you are able to connect the blank on which you are carving. Correct?

I tried doing something similar, but continued to have problems aligning the two sides. I determined that the problem was not with my set up of the spoil board, but with my assumption that everything was aligned perfectly. I determined that it was impossible to get perfect repetition each time this way.

I had a bit of a breakthrough when I realized that I didn't need to have a perfect set up in order to get perfect alignment. Because it was going to be impossible.

What I've done now is to have my spoil board aligned with the origin of my router by drilling a 1/4 v-bit hole at the origin and then a few inches of either side. I think align the CNC perfectly and set the 0,0 by droping the router into the v-bit hole. now I know for sure that my spoil board is perfectly aligned with my CNC.

After that I bolt down my work piece, and cut the first side. Included in my toolpaths are centering holes, they are drilled out at the same time as the rest of the cuts are done, so they are perfectly aligned with the rest of the cuts. Then I use simple wooden dowels in the centering holes (which by the way have matching holes in the spoil board) I turn over the work piece, and because the CNC was aligned with the spoil board, and the centering holes were cut with the same alignment, along with the rest of the cuts, everything is aligned, centered and ready to go on the second cut, without having to spend a lot of time setting up the second side. And, it doesn't matter if the spoil board 'swells' while sitting on the shelf between jobs, because each job realigns itself by cutting the centering holes at carving time.

I hope I haven't confused. lol

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Re: Good material for spoil board?

Postby rscrawford » Thu Jan 12, 2017 5:50 pm

What I have found over the years, is not to make any 'indexing' set-up too permanent. Things change. If you ever make a change to the alignment of your CNC (to square it up), or re-tram your spindle, etc, then all your indexes are off.

So what I like to do is use a cheap MDF spoilboard, and drill all my index holes in maple 'inserts' that I glue into the spoilboard. I cut the maple inserts with a 3/4" plug cutter, and glue them into 3/4" pockets I cut into my spoilboard. Then I drill the 3/8" index holes in the centre of those inserts. If I ever find things out of alignment, I simple pocket out the inserts and glue in new ones, and re-drill my index holes.
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Re: Good material for spoil board?

Postby zeeway » Fri Jan 13, 2017 2:04 am

My two cents: mdf will move, even if you seal it...the location holes you drill, the nicks, etc., must be sealed quickly to keep moisture from getting in...plus you have to seal the back side. Still, mdf is my choice, as well. When I need to index a part on the second side, I cut the index holes for location pins in the same session as the first side. I then put in pins, and flip the part. If I am making more than one copy in the same day, I reuse the pin locations...otherwise, I cut new pin holes.

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Re: Good material for spoil board?

Postby dwilli9013 » Fri Jan 13, 2017 2:43 am

Has anyone ever used slat wall panels for their spoilboard. I have about 15 full sheets that are screaming for me to do this. Just add t-bolts and clamps an you are in business. Could even face down if necessary.
Thoughts??
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Re: Good material for spoil board?

Postby Larry Stobbs » Sat Jan 14, 2017 8:24 pm

I bought an HD4 extended which has been a pain since day one but to protect the top I used MDF cut into 1 1/2 strips and then countersunk the screw heads so that there wouldn't be any chance of a bit hitting them. This allows every other slot in the aluminum table to be open so I can clamp just about any size or shape and the whole thing was pretty cheap to do. I used on 4 x 8 sheet which gave me enough pieces that I could actually make enough to do two tops so if I screw a few pieces up, I can loosen a few screws and replace it in a matter of minutes
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Re: Good material for spoil board?

Postby larrybadgett » Sat Jan 14, 2017 9:55 pm

Anyone tried PVC Foam Board sheets?
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Re: Good material for spoil board?

Postby ChrisInEstes » Sat Jan 14, 2017 10:39 pm

larrybadgett wrote:Anyone tried PVC Foam Board sheets?


I usually use 6mm expanded PVC as a spoil board when I need to cut through material. My router bed is high density PVC (the medium gray stuff) which is held by steel rails, and spaced so I have T-Track slits every 6" across the width of the machine.

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Re: Good material for spoil board?

Postby Olle » Sun Jan 22, 2017 2:09 am

Thanks for the replies, and I apologize for not getting back with you. I'll try and take some pictures, but you can think about it as a pegboard where the distance between the holes changes slightly with the moisture content. The whole spoil board is moving just a little bit, which makes my hole/stud spacing change.

This is more or less a production type setup where I can run 8 sets of pistol grips (16 blanks) in one run. Centering the machine for each blank would be way too tedious so the blanks need to be predrilled and mounted in an exact position. I mill one pair of blanks and move 8" in the x or y direction to hit the next pair. The problem is that the studs won't stay at exactly 8", it will be a few thousands off due to the movement in the spoil board and the offset is exaggerated after I flip the blanks over. If the offset is 5/1000", it will result in a 10/1000" total offset between the parts. It's difficult to explain in words, but the bottom line is that I need a consistent hole spacing in my spoil board.
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