CNC Spoil Board

 
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Old 04-25-2010, 06:53 PM   #1
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CNC Spoil Board


Found this on WoodWeb and if you guys are not using it I think it is a really good and efficient idea.



http://www.woodweb.com/cgi-bin/forum...pl?read=651901

Quote:
Let's look at the extremes.
First, picture a very thin spoilboard. It lets a lot of air pass through it quickly. It doesn’t allow a hard vacuum to build under the board so you don't get any pressure holding your parts down. It still works pretty good if the entire surface of your table is covered with melamine, but as soon as you cut through you get a rush of air equalizing the pressure below and soon the vacuum can't keep up no matter how big it is.
Now picture a very thick and dense spoilboard. No air flows through it, and so no pressure holds the work down. The pump is creating a hard vacuum below the spoilboard, but it is all held in by the very dense and thick spoilboard. A very small pump will evacuate the plenum below the table, but no holding power.
Real life is a balance between these extremes.
Like Roger I used to use Trupan very successfully. I started with 2 layers of 3/4, edgebanded all edges, screwed the bottom sheet down to the phenolic with nylon screws and used up the top sheet bit by bit one almost completely, then switched the top sheet out for another one. I liked the extra distance between my router bit and the phenolic table…just in case. That happened to be on a 4 by 8 table with a 9 HP pump.
Now I use standard MDF, and do like Joe does. I happen to be using 40 HP of pump. I use it from full 3/4, coat the edges with 3 or 4 coats of poly to prevent bleed and skim both sides. I use it down to a little more than 3/8 inch, and then surface it to 3/8 exactly. I put that sheet aside, then use another one from 3/4 down to 3/8. Surface it clean. Put a small amount of regular yellow glue around the edges, put the first sheet back on and let the vacuum clamp it under a sheet of melamine for 10 minutes. Now you have a piece of ¾ again with no waste at all and keep your spoilboard within a good range, a little more than 3/4 to a little more than 3/8.
Everyone has an opinion on this and with an understanding the principles involved you will need to experiment with your system and find that “sweet spot” between all the variables at hand. So much goes into this decision…. pump size, pump configuration (rotary vane pump, regenerative etc….) tooling strategy, part size you want to cut, condition of the surface of the spoilboard, edge sealing, material warp, etc that getting a lot of advice and then choosing your own strategy is all you can do. Keep your mind open and have at it.
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Old 04-25-2010, 11:38 PM   #2
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Re: CNC Spoil Board


Bump, now that Gus is on the board

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Old 04-25-2010, 11:53 PM   #3
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Re: CNC Spoil Board


His method has merit but it seems like a lot of screwing around for something that only needs replacing every 4-6 months. I agree about the high air flow on the thin spoil board and because of it I would never run it down much below 1/2"

For small part machining (such as fluting) I would just screw the part to a larger base and rarely had any issues.

ps Gorilla tape (or any other) works well for edge sealing...keep the poly in the finish room where it belongs
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Old 04-26-2010, 12:02 AM   #4
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Re: CNC Spoil Board


You would think with all of your saddle time with CV the typing speed would've picked up...why you gotta make me wait so long. I need to get to bed
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Old 04-26-2010, 12:08 AM   #5
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Re: CNC Spoil Board


I'm interested in the Tarpon. Have not heard of it and google did little for me.

We find that 3/4 mdf is too thick and loose more small parts than starting with 1/2" and take it right down to 5/16" or so.

We lose small parts when we need to surface the spoils board for more than any other reason. All the little troughs from the previously outlined parts creates a lot of vacuum lose.

I do find a lot of logic in the concept of losing more vacuum through the kerfs as the sb gets thinner. I have not considered that before. And it has not been my experience either. I think the matrix of your phenolic top may have a lot to do with that. Ours has quite the grid to deliver vacuum to the bottom of the sb as much as possible.

I just have not experimented with anything other than mdf.
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Old 04-26-2010, 12:10 AM   #6
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Re: CNC Spoil Board


Quote:
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You would think with all of your saddle time with CV the typing speed would've picked up...why you gotta make me wait so long. I need to get to bed
sorry I was multi tasking. I had to see a man about a horse. And downloaded some material.
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Old 04-26-2010, 12:11 AM   #7
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Re: CNC Spoil Board


How deep are these troughs that you speak of?
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Old 04-26-2010, 12:13 AM   #8
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Re: CNC Spoil Board


.005
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Old 04-26-2010, 12:14 AM   #9
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Re: CNC Spoil Board


Can you catch your finger nail on them?
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Old 04-26-2010, 12:15 AM   #10
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Re: CNC Spoil Board


Yes, but I have false nails
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Old 04-26-2010, 12:17 AM   #11
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Re: CNC Spoil Board


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Yes, but I have false nails
roflmao
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Old 04-26-2010, 12:19 AM   #12
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Re: CNC Spoil Board


Who is typing slow now?
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Old 04-26-2010, 12:22 AM   #13
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Re: CNC Spoil Board


Try dialing in your cutter a little tighter. I assume you are using a comp bit of some fashion. Try to get it set so the only way you can tell a pass has been made is that the mdf looks a little burnished. The little troughs are causing you to lose a lot of vacuum. How often are you resurfacing the spoilboard?

My wife is pissed at me....I gotta go TO BE CONTINUED
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Old 04-26-2010, 12:23 AM   #14
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Re: CNC Spoil Board


Quote:
Originally Posted by Gus Dering View Post
Who is typing slow now?
Who's multi-tasking now
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Old 04-26-2010, 12:25 AM   #15
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Re: CNC Spoil Board


Quote:
Originally Posted by Bergstrom View Post
Try dialing in your cutter a little tighter. I assume you are using a comp bit of some fashion. Try to get it set so the only way you can tell a pass has been made is that the mdf looks a little burnished. The little troughs are causing you to lose a lot of vacuum. How often are you resurfacing the spoilboard?

My wife is pissed at me....I gotta go TO BE CONTINUED
Now there is something I understand.

I'll give that a try tomorrow.
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Old 04-26-2010, 01:09 PM   #16
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Re: CNC Spoil Board


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Now there is something I understand.

I'll give that a try tomorrow.
Pissing off your wife or tuning up your cutter? One will make life better for you and the other will not....... trust me I know
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Old 04-26-2010, 01:10 PM   #17
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Re: CNC Spoil Board


Sounds like both can make life easier>

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