Making Holes for Saw Bolt

[DSEL74]

Counterbore vs Forstner


Thought I have enough info now to give you a informed review

I will write this as someone picking it up off the shelf with the intention of drilling holes for saw bolts.


The only real downfall I found with the counterbore was that with the collar on it used as a depth stop for accurate repeatable blind holes tends to clog up on each hole. It can be quite difficult to clean out more so without removing it from the drill press. The issue with the wood material building up inside the depth collar is difficult to overcome and would be an issue with any drill bit with the collar fitted it is not specific to this drill as the wood builds up between the flutes and the collar. I personally found that I needed to clean out the wood build up after each saw bolt seat has been done to insure full depth of the counterbore is achieved without mishap



The second more minor issue is locating it in the jaws of the chuck. My jacobs chuck can't reach down to the solid section of the shank even with the drill pushed in to it's full depth. Others may have a different experience with other makes/models of drill chuck. So it is fiddly to align the drill so that none of the jaws sit on the slits and put it off centre. This is more or less of an issue dependant on work flow.


I drilled one actual saw handle and several test timbers of various species and fitted bolts.



The way we were instructed to drill the holes at the workshop was to clamp the tote in place, drill a fine pilot hole, followed by 3/16 hole for shank to half depth, then forstner bit. Reposition for second hole and repeat. Flip over align with pilot drill, swap to forstner , then finish the 3/16 and then repeat on second hole. So I similarly followed this process with the counterbore bit. Which is where it would be an issue trying to align the slit in the jaws many times doing it in this process.

I later tried skipping the fine pilot drill, and found it wasn't needed unless you were using very curly hard timber. The reason you can skip this is the countrebore is self centring and you don't need the pilot hole to locate on the opposite side the way you do with the forstner. The counterbore just uses the 3/16 hole.

With the counter bore the with its built in pilot to achieve its role the holes 1st need to be bored straight through with the 3/16 drill bit. Once this step is completed, its quite easy to match the counterbore seats on each side of the saw handle. Where the counterbore pilot remains far superior to that process followed using a forstner bit, is keeping the counterbore seat exactly concentric to the 3/16v stem hole. Without its use, it can make it much more difficult to achieve an even fit with the saw bolt heads.


I also found that once the 3/16 hole was drilled I could quite easliy hand hold while drilling with the counter bore bit and no loss of accuracy again due to the pilot.
This isn't possible with the forstner and still be highly accurate.

The holes tended to be in my opinion cleaner and sharper (better finish) with the counterbore than the forstner. The forstner does clog but probably less than the counterbore and the forstner was easier to clean.

Also on one of my holes some saw dust was sitting on the edge of the collar and it burned on the surface of the hole (see photo), not a major issue as long as your aware and keep it clean. Putting a protective material between the collar and the surface of the tote isn't really necessary if your careful and gentle. If it does leave a light buff mark, which is easily removed in your sanding steps required anyway.
297601

I had no issues with any tearout or rough cutting in any of the timbers I tried the counterbore on, finish was always high. Then it is still new and very sharp, so I can't comment on long term as it gets dull. Then again all bits get dull over time.



Over all I think the counterbore is a better option if your going to make a few saws. As cuts down the steps and fiddling around needed in the process we were shown. I would have no hesitation in recommending it. If you were doing one or two saws and already had a suitable size forstner then probably not needed.

[DSEL74]

297602

This is the counterbore I used the centre pilot drill was removed and swapped for a 3/16 piece of drill rod to be the pilot for alignment. Doing this prevents the the pilot drill from starting an off centre hole on the opposite side.

The 3/16 drill is then used as a regular drill to set the first through hole.

[Isaac S]

To prevent all of the clogging, move the stop collar up a half inch, then use a half inch spacer to get the depth right. The thickness of the spacer is arbitrary, but needs to match the distance you move the collar up. The whole idea is to give the chips somewhere to go, rather than jamming them up into the flutes under the stop collar. Works a treat, as some say.

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Complete details (http://www.blackburntools.com/blog/saw-build-along-handle-part-viii/), with even more pictures, of how I do this.

[DSEL74]

To prevent all of the clogging, move the stop collar up a half inch, then use a half inch spacer to get the depth right. The thickness of the spacer is arbitrary, but needs to match the distance you move the collar up. The whole idea is to give the chips somewhere to go, rather than jamming them up into the flutes under the stop collar. Works a treat, as some say.

297645 297646 297647


Complete details (http://www.blackburntools.com/blog/saw-build-along-handle-part-viii/), with even more pictures, of how I do this.


I remembered you use the spring steel protector, I had forgotten all about the spacer and what it was for. Thanks for the reminder and for all the other reading for the first time.

[Isaac S]

If you are only doing a few saws, the spring steel is not needed. But the aluminum spacer would wear after a number of holes, and would soon lead to inaccuracies.

For just one or two saws, a hardwood spacer would probably work well.

[DSEL74]

Makes sense. Your experience is always welcomed.

[planemaker]

Hi Dale. The un-spiraled section of drill rod are excessively long on these type counterbore/pilots. I am thinking be advantages in cutting off the top split section drill rod closer down towards the existing grub screw. The grub screw could also be changed out to a shorter length so its tightens up below the outside surface of the drill rod. This would make it much easier to position within the chuck jaws.

Stewie;