bit drift

[outcaststudios]

im sure this is a somewhat normal occurrence ,but,today i was cutting one inch thick HDU and about halfway through it 'sounded' different. so i looked closer while it was running (it was towards the end of a 10 minute cut) and saw that the tool was now cutting through the material and into the spoil board. not a big deal ,since i used an onion skin to keep parts still i figured the table was just a hair higher on that side. the thickness of the onion skin is probably about .02 ,enough to hold the part. so its normal for the mdf spoil board to be a little inconsistent(even though i ran a leveling program not too long ago) .i just thought it woudl be about a few thou into the board. when i removed my board i realized that the bit had drifted DOWN in the collet and was now cutting almost another 3/4 into the surface (giving a total cutting depth of 1 3/4!). everything in the file that was being cut was the same toolpath ,and 80% of the cut was fine but towards the end (after the collet heated up i think) it let go and LUCKILY the bit locked back in place. lesson of the day. its better to over tighten than to under tighten. even though i try really hard to seat the collet at just enough torque to hold tight and not stretch the threads or whatever ,its worth the price of a new collet to never have this happen. so my question is this. now that the spoil board is kind of messed up in the middle,can i fill it with durhams ?or non shrinking tooling plastic and re-level it? anyone have any materials they like to fill holes on the spoil board with? thanks!
-gregor

[knight_toolworks]

well it depends on what spindle your using. if it is a had it requires 80inch pounds of torque thats a fair amount. I use long handle wrenches it makes it easier. but the collet could be worn too it's best to replace it then screw something up.

[outcaststudios]

what is teh best material to use to fill the voids in the spoil board? im hesitant to use anything that will 'wet' the mdf. what do people use for this?

[steve_g]

Durhams works well… but the moisture will locally swell the MDF and require spot leveling after dry. If you just can’t live with the divot, epoxy also works.
SG

[knight_toolworks]

or what I do bondo fast and easy and stinky.

[gundog]

Here is something to think about never bottom a bit out in the collet always leave a little space because as you tighten the collet it pulls the bit up if it can't move up it wont get as tight and I would for sure toss the collet.

[jTr]

Hate to be contradictory, but I'd avoid any fillers/putty products, considering the depth of grooves (1 and 3/4", right?). Any product I can think of would unlikely pass the much needed vacuum into that area of your table.

Use MDF of the proper thickness to fill the void based on kerf (bit) diameter. Be aware this may create some reduction in vacuum pull, depending on porosity of the material used. Optimally, use a scrap of ultralight MDF if you have it. A dab of glue at the bottom of the kerf is all you need to tack these plug strips in place. This way, your table can perform more predictably in terms of vacuum pull and even distribution.



Jeff

[jerry_stanek]

I keep some mdf dust to mix with some glue and use that for my fill

[guitarwes]

This happened to me once after cutting a few runs of UHMW. I was cutting some thru holes on some pieces and I noticed the bit was skimming the surface when it would lift up and move to a different hole, only about 30-40 thousands. When it would drill a hole it was cutting down into the spoilboard .25" (the amount of my Z pullup). I contributed the bit slippage to the vibration it causes when cutting UHMW for long cuts.

[gundog]

I have put patches in my Trupan spoilboard with a scrap piece of Trupan left over because my Vac table is 54x96 so I always end up with extra when I get 4x8 sheets. I just pocketed out the damaged area and cut a piece to replace it glue it in and surface the whole table.

Mike