Practice build: 5-string multi-scale, HD woods

[iamlowsound]

Looks good! What order are you drilling the holes in? If you are drilling the small hole first, I see no reason why the larger hole would skew off centre.

lowsound

[IntrepidCellist]

The only way I can think of to avoid decentering would be to do it (carefully) by hand with a dremel, or else glue the knob to a block, drill it, and then cut the knob off.

[Keith Guitars]

Hole skewing can be a real bear. A few thoughts:

Try drilling the larger hole first. Sometimes, especially with holes that are not very different in size, the smaller "pilot" hole will cause the larger bit to want to just screw into the work rather than cutting, which can cause this skewing issue.
This is why machinists' reamers typicially have no shear angle - if they did, they would just thread themselves into the work instead of cutting.

Doing this will also allow you to file a smaller flat, which can catch the tip of the bit to center it, but gets wasted away once the full diameter hole is started.
The smaller bit will self-center in the cup-shaped bottom recess left behind by the larger bit's tip.

SHARP drill bits. Mcmaster-carr sells them pretty cheap, as does Enco. So very worth it, for about 3 or 4 bucks a pop.

A brad point bit won't help at all if the center is already drilled out.
Turn up the RPMs also, to whatever extent that's possible.
A larger, more rigid bit such as a Forstner bit may also help.

Obviously, drill both holes before cycling to the next part. Leave everything clamped up and don't move the part until both holes are drilled. It means two tool changes per part, but it's worth it to get a good result. Maybe use a stronger clamp.

Failing that, consider using a center-cutting end mill chucked in your drill press to drill the larger hole. They are much shorter (and thus stiffer) and therefore have less tendency to wander. The face (tip) is also flat and would cut a square-bottomed recess, which might prevent the round ball end from wedging in there and getting stuck or even splitting the part. If I were doing it that way, I'd drill out the smaller hole first, so the centermost part of the mill wouldn't have to do any actual cutting - the tool speed there is really low and it wouldn't be very happy.

Finally, if all else fails - drill the holes first, then cut out the plugs. It means careful measuring, but it would work for sure.
Maybe use one flat side of the piece of stock to index it against a common fence for all three operations, so you stay aligned in the critical axis. That way, you only have to be careful to locate the tenon cutter in the right place for the correct depth of recess.

Best of luck,
Martin

[pilotjones]

Originally Posted by Keith Guitars

Hole skewing can be a real bear. A few thoughts:

Try drilling the larger hole first. Sometimes, especially with holes that are not very different in size, the smaller "pilot" hole will cause the larger bit to want to just screw into the work rather than cutting, which can cause this skewing issue.
This is why machinists' reamers typicially have no shear angle - if they did, they would just thread themselves into the work instead of cutting.

Doing this will also allow you to file a smaller flat, which can catch the tip of the bit to center it, but gets wasted away once the full diameter hole is started.
The smaller bit will self-center in the cup-shaped bottom recess left behind by the larger bit's tip.

SHARP drill bits. Mcmaster-carr sells them pretty cheap, as does Enco. So very worth it, for about 3 or 4 bucks a pop.

A brad point bit won't help at all if the center is already drilled out.
Turn up the RPMs also, to whatever extent that's possible.
A larger, more rigid bit such as a Forstner bit may also help.

Obviously, drill both holes before cycling to the next part. Leave everything clamped up and don't move the part until both holes are drilled. It means two tool changes per part, but it's worth it to get a good result. Maybe use a stronger clamp.

Failing that, consider using a center-cutting end mill chucked in your drill press to drill the larger hole. They are much shorter (and thus stiffer) and therefore have less tendency to wander. The face (tip) is also flat and would cut a square-bottomed recess, which might prevent the round ball end from wedging in there and getting stuck or even splitting the part. If I were doing it that way, I'd drill out the smaller hole first, so the centermost part of the mill wouldn't have to do any actual cutting - the tool speed there is really low and it wouldn't be very happy.

Finally, if all else fails - drill the holes first, then cut out the plugs. It means careful measuring, but it would work for sure.
Maybe use one flat side of the piece of stock to index it against a common fence for all three operations, so you stay aligned in the critical axis. That way, you only have to be careful to locate the tenon cutter in the right place for the correct depth of recess.

Best of luck,
Martin

Thanks for the info. Unfortunately, I didn't adequately describe the process I used, so some of this didn't apply.

Here's what was missing, plus a few other points.
- I drilled the large hole into virgin wood, intentionally not doing the small hole first so as to have wood there for the brad point to dig into. I thought that point would hold the bit in line until the wings were fully engaged, but I guess not.
- The bit was run at the max recommended RPM from a chart I have, I don't recall offhand what that was
- I actually flipped the piece over after this and drilled the small hole from the other side, so that the breakout was internal to the part
- I had previously done a few knobs by pre-drilling the holes, then running the tenon cutter. Unfortunately, some turned out well and some badly. I believe this is because it's hard to line up the tenon cutter, it being hollow in the center. I had laid out a crosshair on the center point, and lined up the four cutter wings on the bit with the lines. I did what I thought was a decent job, but any inaccuracy may have combined with the #%$*@%$# play in my spindle and any unevenness in the entry surface, causing the cutter to bite on one side first, skew, and then continue to follow that path.

I may have to look into getting a small end mill. I don't believe they make Forstners in .281".

[mbelue]

Pilot this build log has been my favorite diversion for some time, thank you for sharing.
About your anchors. Just trying to think outside the box, maybe your problem isn't the drilling sequence. Could you make the necessary holes in a larger square block and then cut them into appropriate size and shape?

[pilotjones]

Originally Posted by mbelue

Pilot this build log has been my favorite diversion for some time, thank you for sharing.
About your anchors. Just trying to think outside the box, maybe your problem isn't the drilling sequence. Could you make the necessary holes in a larger square block and then cut them into appropriate size and shape?

Thank you. Glad you like it.

Tried what you suggest already, see bullet point #4 above.

[mbelue]

Oops sorry about that, my lack of trade vocabulary got the better of me.

[pilotjones]

Tonight I mostly reworked the bridge layout. A lot of measure, think, erase, draw, observe, think, repeat half a dozen times.

The result is something I think I like.



I'm getting more and more inclined to change as little as possible when build the second bass. There's a whole lot of fixture making and figgerin' that I'd like to avoid!


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I also made up another batch of "padauk tea" since I was running low. I just love the colors of the stain as it dries!

[roberthabraken]

Enjoying every post of this thread. I like your techniques and bridge design! Your play in the drilling could very well be that of the drill itself, but I do not have enough experience on this matter so I'll leave it with that..

[Kirk Bryant]

I've only read about 20 pages but I'll come sweep your shop for minimum wage now if you like!

P+L Kirk

[Dave Higham]

You could try to make a drilling jig.

Take a block of maple slightly less thick than the height of your posts, and drill a hole in it that your posts will just slide into. Drill a hole through into this hole the diameter of the larger of the 2 holes you want in your post but not through the other side. Fix a piece of wood to your block effectively making the post hole a blind one. You now have a drilling jig that you can slide your post into and clamp it to stop it moving. Align the jig with the drill on your drill press and clamp it in place. Slide your post into the jig and clamp it endways (axially?). Drill the hole for the ball end first and then the hole for the string. The fact that you only drilled the ball-end hole half way through means that you have support when drilling the string hole which should prevent break-out.

Hope this makes sense and helps.

[Dave Higham]

A picture's worth a thousand words, and as you're an engineer .....

[pilotjones]

Thanks for the compliments, guys.


Dave, thanks for the idea and the effort in making a drawing. I had previously entertained doing a drill jig,and dismissed it. Now I may try something like your plan.

[Darkstrike]

Originally Posted by pilotjones

I also made up another batch of "padauk tea" since I was running low. I just love the colors of the stain as it dries!

Dang, that rag is one of the nicer Sunbursts I've seen!

[mikebpeters]

PJ, I've been thinking about your skewing problem. Admittedly I haven't gotten to that point in my own knob construction, but my plan was to use the simple jig that I built to repeatably drill holes for the 2mm abalone markers in the top of my knobs. I use a 3/4 tenon cutter, so I just used a 3/4 forstner bit to drill a hole in a small block of wood. The knobs fit snuggly in the hole.

My plan for the last bit was that I was going to carefully mark and drill a pilot hole in the side of my block to use for centering my set screw holes. I haven't tried it yet, but the jig worked admirably for the top holes.

I rather expect my jig to wear, but hey, its three holes in a piece of scrap so even if I only get one set of knobs from a jig I'm happy.

[pilotjones]

Good to know a jig something like this worked for you.

I've got an idea for a small trick to reduce the wear on a wooden jig. I'll let you know if it works out to be a good idea.

[Dave Higham]

Originally Posted by pilotjones

I've got an idea for a small trick to reduce the wear on a wooden jig.

Like, perhaps, incorporating a string ferrule?

[mcblahflooper94]

Long time lurker, first time poster... I think it would be a good idea that when the bass is finished, so we don't have to cram it all in one huge thread, you make a new thread just to show it completed.

[pilotjones]

Originally Posted by Dave Higham

Like, perhaps, incorporating a string ferrule?

That would be a great idea, if my counterbores were sized the same as the ferrule IDs. You would just cut or grind off the inside lip. Great thinking! Unfortunately, my counterbores at present are just a touch larger than the ball itself, and I think ferrules have a bit more free space. Can anyone tell me a typical ID of one of those ferrules?

Originally Posted by mcblahflooper94

Long time lurker, first time poster... I think it would be a good idea that when the bass is finished, so we don't have to cram it all in one huge thread, you make a new thread just to show it completed.

I thought about that. What would be the benefits? If it's just to allow easy navigation to the pics, I could also edit post #1 to include a link to the first post with the final pics. Thoughts?

[pilotjones]

Originally Posted by Darkstrike

Dang, that rag is one of the nicer Sunbursts I've seen!

I know, it's fantastic. It eventually dries to a fade from the dark orange to a darker brick red. I call it sunsetburst.

This stuff also turns purple in contact with iron.