Dedicated and Gasketed Spoilboards

      Advice on spoilboard refinements for holding down small parts during CNC machining operations. August 17, 2006

What’s a dedicated spoilboard? What’s a fixture spoilboard? What is “gasketing the spoilboard” and how do you do it? I have a Weeke BHP 200 and I’m having problems holding little parts. I resurfaced both sides and I painted the edges. Are there different types of spoilboards? Where do I get them? We are a southern CA retail fixture shop.

Forum Responses
(CNC Forum)
From contributor A:
When you resurfaced your spoilboard, what tool did you use? We recommend an Insert with feed speeds at 1000 IPM. This leaves a fir (hair) on the material, which assists in holding smaller parts. With a nested based production you will have to resurface the spoilboard, as grooves will form and parts will move. I'll let others give a more technical answer on the different types of spoilboards. On a final note, use a down shear tool, which again will assist in smaller part movement.

From contributor B:
To the original questioner: We also have a BHP 200. What vacuum do you have? Do you have the phenolic "otrix" table?

From contributor C:
A dedicated spoilboard is one that is created to hold one specific part or component. A fixture spoilboard is one that relies on components in addition to vacuum to hold a specific part(s) - components such as toggle clamps or pneumatic clamps. Gasketing a dedicated spoil is a process where you place a seal gasket trough in the spoil. Say your component was very odd shaped around the periphery and gets routed around the periphery, then you would create a program, slightly inset to the finished periphery of the part (a scale feature on most CNC machines is great for doing this) and route a trough or channel to place gasket material. Then you would drill a hole through the center area in which to plumb vacuum or use the auxiliary vacuum features found on most router/point to points. Spoils of this nature are very effective. You are only limited to your imagination.

From contributor D:
Try onion skinning your parts. It will greatly reduce part movement. It also depends on what kind of material you are running at how small of a part and how many are nested together you can hold down. I am not sure about your machine but a lot of machines are vacuum zones. With some you can add some of your vacuum power to one zone or another for better suction. What is your primary material that you are routing? Also, an onion skin is when you router your parts - you down a first past that stays above your spoil board a 1/32” or 1/16” and after all the rough cutting is done come back on the same program and final cut. This is the most typical way to minimize part movement.

From contributor E:
I would just add that it's not always necessary to rout a trough in the fixture. If the gasket material is dense enough, or the part being cut is not height or profile specific (cutting and odd shaped part to size), then you can put down gasket tape directly to the main spoil board and drill a small hole for vacuum. We do this routinely, and then fill the hole in the spoil board with hot glue when we're done.

From contributor C:
To contributor E: Good point. Other advantages of the method described are that you can make sound, functioning spoilboards rather quickly and comparatively cheaply. Also, often I encounter people who may only want to drill a series of holes or rout on a very small part (let's say 2" x 2" x 6" - rectangular). For some reason the common misconception is that they have to clamp in some fashion because there is not enough surface area on one face to effectively make a spoil. Who said you have to spoil to only one face? In this instance, you can make a right angle spoil or a channel spoil and seal and route vacuum to 2 or even 3 faces if needed.

From the original questioner:
I have been using the onion skin method but it really lags especially when there are about 30 sheets to cut. I mainly cut plywood and double-sided laminate stuff. I’m not sure what type of vacuum we have but I know it’s supposed to be plenty for what we do.

From contributor D:
I understand what you are saying. We also do a lot of two sided p. lam material. And I understand the time per sheet factor, but you have to ask yourself the question “Do I slow down and onion skin and get a better yield or do I run with through cuts and take a very good chance of damaging the product and maybe the machine”. If you figure how long it would take for a man on a saw compared to what it takes your machine to rout out parts, I am sure you will find you are still very much in the good by onion skinning.

From contributor E:
Be sure to check the air filters between the machine and vacuum. If they get clogged then the vacuum won't work. Depending on your application, you might need to clean them every other day, or maybe every other week.

From contributor D:
I agree we clean our filters everyday, but we are running at less than a unit on material a day also. Any filter on your vacuum system is very important to keep as clean as possible at all times. Inspect you hoses as well while the vacuum is on. I have seen them collapse from time to time.

From contributor F:
For you guys that do an onion skin, what bit do you use? I almost always use a .25 diameter bit upcut, downcut or compression, cutting .5 or .75 MDF. When I cut small parts I almost always get a ridge where the first cut depth ends and where the second through cut cuts. It's just a tiny difference and it usually is proud all the way around the part. You can't feel it but it just keeps the parts from a good flush fit.

Now that I think about it, I can do the first pass as a rough cut to depth and a clean pass to through cut. What do you think? I'd really like to know what causes this. My only guess is bit deflection. Should I re-toolpath everything to a 3/8 bit?

From contributor B:
The BHP 200 we have has a phenolic table that does not require a gasket - it's not a matrix type table. Ours has reverse air and we work with two spoilboards at a time. We cut a 2mm deep grid on the underside of our spoilboards, and that lines up with the holes in the table. This helps to distribute vacuum to all parts of the board evenly, as a manifold is essentially formed by the grid. Of course, we seal the edge of the spoilboard. We band ours with 3mm PVC. This seals the edge and prevents damage that might occur when rotating spoilboards using moblie tables. Cleaning the filters will help, however only a small percentage of vacuum is lost on our machine when the filters are dirty. I should mention our machine came with a 25 hp Dekker vacuum, and there were some leaks in the system under the table that were fixed by Weeke. You might want to pull the panels on the sides and check the manifolds under the bed.

From contributor D:
When we got our router we started off using a 0.375 compression bit for all of cut out operations. And quickly went to a 0.5 compression for melamine, particle board and MDF but on plywood we use a 0.5 straight bit but about half of the feed rate of the compression bit. The reason why we use the straight bit is because a compression bit leaves a lot of fuzz on the edges. We edgeband most of our product and the fuzz will telegraph thru if you are using PVC edge banding. We also switched over to using 1mm PVC also instead of the standard 0.5mm PVC. Basically the straight bit leaves a much cleaner cut. We have not noticed much of a difference in the speed of the sheet operation by using the straight bit. We also experimented with style of bit, but have found that a standard compression bit works best, because of the cost or re-sharpening and durability. We use a down spiral 0.25 bit for doing dados and rabbets only. Also the 0.5 will have much less deflection than most. I know of a local company that uses 0.75 bits, but most of the cabinet shops in this area use only 0.5 bits. Experiment with different sizes and speeds and see what works best for you.

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