[member=53696]Roachmill[/member] - Thank you so much for your most thorough reply!
This very telling picture of yours:
...says it all!
Based on it, it's now clear to me that my idea for how to add dust collection to this drill guide is totally doable.
Now, in order to counter your concern over what you characterize as "bad news", I have a different take.
1/4" (6mm) Plexi Overlay
If desired, selecting 1/4" (6mm) thick plexi for construction of the removable overlay will in effect swallow up almost all of the height of each vee guide. Corresponding slots milled through the overlay in the relative locations of the vee guides would serve to essentially eliminate them as obstructions. In the case of the rear vee guide, the remaining ~2mm of it sticking up above the top surface of the overlay would fall within the free area under the shroud (so no conflict there in terms of an obstruction). Now, if needed, a little cap of plexi sized to encapsulate the slot at the rear (with a couple of shallow flat bottomed holes drilled in it to account for the sharp points of the vee guide sitting proud of the top face of the overlay) could be glued in place to hermetically seal the slot. Or (and I'm guessing that this might the case) both vee guide slots in the overlay could simply be left as-is since, practically speaking, I don't think there would enough suction loss at the location of the rear vee guide to warrant any additional effort.
The matter of the four raised cast slots in the base, on the other hand - which are intended for mounting of the vise - could be easily addressed by marking their location on the underside of the overlay and then simply machining corresponding ~2mm deep oval-shaped shallow depressions into the underside of the overlay into which those raised slots would fit (thus allowing the entirety of the overlay to lay perfectly flat and unimpeded onto the top surface of the base).
1/8"(3mm) Plexi Overlay
Alternatively, in order to reduce the amount of milling required to produce said overlay, 1/8" (3mm) plexi could be used instead. If this thinner material will fit underneath the two guide rod pillars (
Question: If possible, I need to know the corresponding amount of headroom as depicted below):
View attachment 1
...then this would also potentially greatly simplify the overlay's overall design. But, given the thinner nature of this material, extra care would need to be taken to ensure that the oval depressions milled into its underside (to account for the profiles of the raised slots) don't puncture all of the way through the overlay. If this is a problem, thru-slots could be milled instead and a second duplicate overlay (which omits the slots) could then be stacked on top of (and adhered down onto) the primary overlay. The perimeter of this duplicate overlay could be shaped slightly differently in order to prevent a conflict with the full range of travel of the guide rod pillars while also maintaining enough remaining surface area over the aperture for the shroud to suction down onto. This would bring the overall thickness of the overlay up to a 1/4" (6mm) but that shouldn't be a problem.
On/Off Installation/Removal of Overlay
To facilitate easy on/off of the overlay, countersunk holes and four flat headed screws could be used in conjunction with the threaded holes machined into each corner of the base to allow the installation to be performed from above. Said another way, I didn't realize at first that those countersunk holes in the base are threaded but knowing now that they are would allow the overlay to be fastened down from above. At first, I considered the use of thumbscrews but since, as is shown in your photo, their tall profile would conflict with the rear end of the dust shroud it makes better sense to simply use flush mounted flat-headed screws at all four fastening points. Tool'less installation would be nice but we can't have everything! That said, maybe employing the use of a different suction shroud would ultimately allow the use of four thumbscrews.
Now, if one is going to employ the use of a sub-base (say, in lieu of the guide's problematic non-slip rubber pad), then the four threaded holes won't necessarily be available for use as the attachment method (unless, that is, the length of the fastener chosen allows
both the sub-base
and the overlay - the latter in conjunction with four threaded inserts - to be co-installed from the underside). However, if this is going to be the case, then to reduce the added-complexity the idea I originally had of utilizing the four cast slots in the base in conjunction with four threaded inserts in the overlay for mounting the overlay from underneath might work better.
Length of Overlay
Finally, its good to know that the rear end of the overlay will not need to be asymmetrically-sized to cantilever-out off the rear end of the drill guide's base
all that much. I assumed that it would require quite a bit of overhang but your photo shows that only a little overhang will be necessary.
Thanks again!
