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Old 06-26-2020, 09:15 PM
jtogg jtogg is offline
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Default Holdin' It Down

I need to implement a system for holding down the spoilboard and workpieces on my vacuum-less Stinger. Obviously others have solved this problem many times before but I figured I’d open my approach up for feedback and document the process for others. I’m pretty averse to the idea of repeatedly glueing spoilboards to the factory phenolic, and know others use nylon screws for this purpose. I considered adding more T-track for securing workpieces but I figured more nylon screws would be safer to run into than clamps and require less Z movement to avoid. I’ll also be doing lots of two sided jobs and this should make registration easier. Anyway the plan now is to:

• Use the CNC to drill a grid of thru holes with 4-1/16” spacing (consistent with my T-slot rail spacing).
• Drill a second grid between those holes. (All holes directly above the machine frame will be drilled blind)
* Remove the factory board, drill out blind holes by hand and add shallow counterbore.
* Install flanged 1/4-20 threaded inserts (https://www.mcmaster.com/92105A300) in all holes from underside of factory board. Reinstall on machine.
* Clamp down three 3/4” MDF spoilboards between the T-slots.
* Drill the first grid in MDF (1/4” thru holes and 1/2” deep counterbores)
* Drill the second grid (1/4” thru holes)
* Install 1-1/4” nylon screws in counterbored holes to hold down spoilboard

The empty grid of holes will accept either longer nylon screws for holding down workpieces, registration dowels, or the same clamps that come with the T-slots. 1/4” of material under the screw heads should leave 1/4” of SB planing before screw heads start to get shaved down (Could do metal screws with thinner heads for more planing depth and and greater risk to bits). There may be jobs where I end up just screwing workpieces down into random spots on the spoilboard, but bolting into the grid should keep the SB cleaner and free of volcano-shaped screw holes. If needed, I can mount smaller or more expensive workpieces to a second board which then gets mounted to the 4” grid.

Thoughts? What did I miss? I’ve read about and will freshen up on the soft limit issues when drilling past Z zero. Any and all advice appreciated!





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  #2  
Old 06-27-2020, 10:08 AM
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james mcgrew james mcgrew is offline
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Im pressive graphics !!

Look to make a grid tod capture Vacuum then try a spoil board. (unless I missed something

https://www.youtube.com/watch?v=oP_PqTZABZk

https://www.youtube.com/watch?v=UVBNmtRIckU

You can also use "onlay tables for specialized parts without vacuum

https://www.youtube.com/watch?v=JEJ6rRgFfT4&t=19s
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fixed 4-27-2020
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Old 06-27-2020, 10:16 AM
Jim Becker Jim Becker is offline
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That's certainly a great method to create a predetermined hold down setup and isn't uncommon on smaller machines.

Honestly, I use screws most of the time along with clamps in tee tracks when the spacing is amenable to that. :)
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Old 06-27-2020, 12:31 PM
Jimwill52 Jimwill52 is offline
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I did the same thing with my table-top. I didn't put quite as many holes but the threaded inserts are great. I often use a piece of .5 MDF to screw onto the table as a spoilboard. Nice drawings!
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Old 06-28-2020, 10:37 AM
mike.davison mike.davison is offline
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Will the T tracks at the edges -- only held down on 1 edge -- be sufficiently held? seems like they might rotate and come loose.
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Old 06-28-2020, 03:07 PM
Charlie_L Charlie_L is offline
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Good point Mike.

I found a track in the x direction in the black non-machining area about three inches from the spoil board very helpful. On the opposite end it wouldn’t work for me as shown. Move it up a few inches in the y direction?
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Old 06-30-2020, 11:49 AM
jtogg jtogg is offline
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Quote:
Originally Posted by mike.davison View Post
Will the T tracks at the edges -- only held down on 1 edge -- be sufficiently held? seems like they might rotate and come loose.
Quote:
Originally Posted by Charlie_L View Post
Good point Mike.

I found a track in the x direction in the black non-machining area about three inches from the spoil board very helpful. On the opposite end it wouldn’t work for me as shown. Move it up a few inches in the y direction?
Thanks for the replies everyone. This is helpful.

The T-tracks as shown in my model are as the machine came. I've seen some Stinger owners' photos with different track locations but this seems to be how they're doing it now - without any custom request anyway.
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