Ultra Thin Hole Saw for Cutting Covers?

[BassHappy]

Hey Folks....

I tried using a 3.75" hole saw to do some grain matching covers. Unfortunately, the cutting walls of the hole saw were standard size, which is quite thick. I think a lot of the hole saws available are not designed to provide a thin cut. Additionally, the hole saw was not very stable in the drill press and that added a bit of give. Perhaps the one I got was not great quality:

I would like to find or have machined a 3.75" hole saw with a super ultra thin blade, so that in the end the inner cut-out portion would fit snug and create a cool grain-matched cover.

I am not sure they exist. Perhaps a standard hole saw could be modified or filed down in some way to make the cutting blade edges uber thin? I only need to go max 1/4" deep. Mine seems multipurpose - like it could be used on metal and other materials. Looking for a specialty tool.

Maybe not quite razor blade thin, but as thin as possible - thin enough that the blade would still gently cut through maple, mahogany, ash, walnut, butternut, etc. Maybe using carbide or diamond dust?

@Bruce Johnson - do you have any ideas on how to solve this, or is this a tool you could create - or modify from an existing one?

 

[T_Bone_TL]

I think you are basically going to have to have one ground specific (or grind one specific) or else you (warning, tool that needs a LOT more respect that some folks give it, to their regret) use a fly cutter with a bit ground narrow (easier to grind, but be very very careful in use.)

 

[Bruce Johnson]

Hello Rick;

Yeah, you're not going to find anything off the shelf to do that. It's a custom machining job. Not real difficult; some lathe time and an indexer in a mill to cut the teeth. No need for carbide or diamonds; just a steel saw. A bigger version of one of these:

Basically, you start with a 4" diameter slug of steel, an inch long. Machine the center to attach a 1" diameter steel slug to be the arbor; turn the back end of that down to 1/2" to go in your mill chuck. Pop that in the lathe and turn the front face into a thin sleeve of 3.750" OD x 3.690" ID (0.030" wall) x 1/2" deep. Slight relief undercut on the inner and outer walls. Then set it up in the spin index fixture in the mill and cut the teeth. You don't need a zillion teeny teeth; I'd probably cut 24 teeth, since it's the standard wheel on the spin index fixture.

No need to harden it or grind it. Mild steel saws like this will cut wood just fine, in small quantities. You're not looking to cut tens of thousands of holes. An unhardened mild steel hole saw will cut hundreds of holes before it needs cleaning and sharpening. And it can be easily sharpened by hand with a small file.

Because of the diameter, you'd want to use this bit in a milling machine, or a big drill press that can go down real slow, like under 150 rpm. The body would need to be clamped down solidly, to make sure the saw doesn't skitter as it enters the wood.

If I did this, it would be about $200 to make up a custom plug saw like this; about 5 hours of machine time. I'm pretty busy these days, and not sure I could fit it in right now. Any competent machine shop should be able to make this for you. But you can get back to me if you really can't find anyone.

 

[Bruce Johnson]

I think you are basically going to have to have one ground specific (or grind one specific) or else you (warning, tool that needs a LOT more respect that some folks give it, to their regret) use a fly cutter with a bit ground narrow (easier to grind, but be very very careful in use.)

Well, in the metalworking world, there's a process called Trepanning. It's like a fly cutter; a single thin bit out on the end of an arm, spinning around. It's used to cut a shallow circular groove in a surface, or it can be used to cut a precise disk from a sheet, with no hole or mark in the center. That's fine for metal, but you wouldn't want to try that on fine wood. It would rip up the wood as it crossed the grain.

No, the best way to cut this is with a thin wall custom hole saw, tightly held, slow speed.

 

[Bruce Johnson]

Geez, I forgot all about this one, a custom 1" dia plug cutter/hole saw that I made up for Tom a while back.

looking for a 1" plug cutter bit

This is another example of how to make one of these cutters. It's made as a sleeve that goes on to an arbor. It comes apart to make it easy to get the plug out of the inside. The same basic idea could be scaled up to 3.75" and thin wall of the saw. The cut disk would be captured inside the saw, and you'd take it apart to get the disk out safely.

And, like we did on Tom's cutter, the OD could be machined to ride in a maple guide block, to make sure that it doesn't skitter as the saw enters the wood.

Tom never posted a followup on the thread, but I've heard from him that the cutter works very well.

 

[Jisch]

My dad used to have a hole cutter for the drill press that basically had a blade that could be fixed via a set screw along a beam. I searched and found this, which is similar, but a lot higher tech than the one my dad had. The cutter could definitely be made narrower. (edit and you'd have to remove the center drill (unless you made that hole a feature) which would make this a somewhat scary operation)

Hole Cutter 2-12"

If you're putting a front on your instrument you can cut the cover out prior to putting the front on using a thin blade in a scroll saw, I would avoid trying to make a perfect circle, but I've had good luck with that method.

 

[BassHappy]

Hello Rick;

Yeah, you're not going to find anything off the shelf to do that. It's a custom machining job. Not real difficult; some lathe time and an indexer in a mill to cut the teeth. No need for carbide or diamonds; just a steel saw. A bigger version of one of these:

View attachment 2973710

Basically, you start with a 4" diameter slug of steel, an inch long. Machine the center to attach a 1" diameter steel slug to be the arbor; turn the back end of that down to 1/2" to go in your mill chuck. Pop that in the lathe and turn the front face into a thin sleeve of 3.750" OD x 3.690" ID (0.030" wall) x 1/2" deep. Slight relief undercut on the inner and outer walls. Then set it up in the spin index fixture in the mill and cut the teeth. You don't need a zillion teeny teeth; I'd probably cut 24 teeth, since it's the standard wheel on the spin index fixture.

No need to harden it or grind it. Mild steel saws like this will cut wood just fine, in small quantities. You're not looking to cut tens of thousands of holes. An unhardened mild steel hole saw will cut hundreds of holes before it needs cleaning and sharpening. And it can be easily sharpened by hand with a small file.

Because of the diameter, you'd want to use this bit in a milling machine, or a big drill press that can go down real slow, like under 150 rpm. The body would need to be clamped down solidly, to make sure the saw doesn't skitter as it enters the wood.

If I did this, it would be about $200 to make up a custom plug saw like this; about 5 hours of machine time. I'm pretty busy these days, and not sure I could fit it in right now. Any competent machine shop should be able to make this for you. But you can get back to me if you really can't find anyone.

Hey Thanks Bruce!

I will check with my neighbor Jon, he may be able to do this for me. Not sure how thin you could go with the cutting part before you get in dangerous territory.

Really appreciate it.

Rick

 

[BassHappy]

My dad used to have a hole cutter for the drill press that basically had a blade that could be fixed via a set screw along a beam. I searched and found this, which is similar, but a lot higher tech than the one my dad had. The cutter could definitely be made narrower. (edit and you'd have to remove the center drill (unless you made that hole a feature) which would make this a somewhat scary operation)

Hole Cutter 2-12"

If you're putting a front on your instrument you can cut the cover out prior to putting the front on using a thin blade in a scroll saw, I would avoid trying to make a perfect circle, but I've had good luck with that method.

Wow, what an interesting tool. Never seen anything like that before! Thanks, Jisch!

 

[Bruce Johnson]

Hey Thanks Bruce!

I will check with my neighbor Jon, he may be able to do this for me. Not sure how thin you could go with the cutting part before you get in dangerous territory.

Really appreciate it.

Rick

I'd recommend about a 0.030" wall thickness for the saw. That's about the gap that you'd want around the cover anyway.

 

[rudy4444]

Basshappy, I know you've reviewed my entire build thread, but you might check out the way I did grain-matching covers on my plates. The mechanics of the cut-out are shown in step #93:
30” Scale Compact Semi-acoustic Fretless Bass Build

 

[pilotjones]

I'd recommend about a 0.030" wall thickness for the saw. That's about the gap that you'd want around the cover anyway.

Rick, if you have this made up, just keep in mind that the teeth will have no set. It is the tooth set in the standard hole saw that causes the too-wide kerf, but which also allows chips (sawdust) to clear. So, plunge a little, back out and blow out dust, and repeat. This will keep the steel cool, and prevent turning wood into smoke instead of sawdust, and also scorching the good wood that you want to keep.
- Keep the walls to not too much longer than the depth you will be cutting, both for stability and for better conduction of heat away from the the teeth to the back disk area.
- You want the teeth fine enough that the cutting is shared by many teeth, but not so fine, as in hacksaw-fine, that the gullets between the teeth immediately clog with dust. Remember that the sawdust has no place to go, and once those spaces are filled up, the dust will pack into a sort-of MDF which then rubs and heats up.
- Have them mill several holes through the back disk that are large enough for you to poke through a pencil with a rubber eraser to pop out the disk if it gets stuck. This also serves to keep the wooden disk from being "vacuum locked" into the cup of the saw once it is free of the board.

 

[Bruce Johnson]

Rick, if you have this made up, just keep in mid that the teeth will have no set. It is the tooth set in the standard hole saw that causes the too-wide kerf, but which also allows chips to clear. So, plug a little, back out and blow out dust, and repeat. This will keep the steel cool, and prevent turning wood into smoke instead of sawdust, and would also scorch the good wood that you want to keep.
Keep the walls to not too much longer than the depth you will be cutting, both for stability and for better conduction of heat away from the the teeth to the back disk area. Have them mill several holes through the back disk that are large enough for you to poke through a pencil with a rubber eraser to pop out the disk if it wooden if it gets stuck.

Yes. Now, I (or your machinist) can put some set in the teeth, if you like. Like PilotJones says, that will widen the kerf. On thin wall plug cutting saws like this, I usually don't. I prefer to relieve the walls, inside and out, by a few thousandths, just behind the tips of the teeth. For example, the tips of the teeth are 0.030" wide; 3.750" OD x 3.690" ID. About 0.100" back from the tips, the diameters go to 3.745" OD x 3.695" ID. Behind the teeth, the wall thickness of the shell is 0.020". This has the same purpose as setting the teeth: it keeps the wall of the saw from rubbing against the wood and heating up.

Also, I like to use fewer, larger teeth for saws like this. It helps to clear the chips out and keep it cooler, plus it makes it easier to resharpen. I'm thinking 24 teeth for this 3.75" saw, but maybe even 12 would be better. If necessary, I'll file the gullets (the notches between the teeth) extra deep to help clear the chips.

I also make the back relief of the teeth pretty shallow, as you can see on those cutters above. This limits how much each tooth can take per mouthful, so it doesn't dig in and rip up. I want a cutter like this to go slowly.

With a plug cutter of this size, I don't recommend backing up and trying to reinsert it. Unless you have it really tightly fixtured in a milling machine, there's too much chance of it kicking and chewing up edges of the cut ring. Bring it down to contact and push it quickly down to the full depth.

Did we mention that you need to put a clean piece of MDF underneath?

I'm assuming that the sequence is to cut the matching plug from a 1/4" thick sheet of gorgeous wood, which then gets glued onto the back of the body, positioning the hole over the cavity that's pre-routed in the body center wood.

 

[mikewalker]

Our shop sometimes used to cut continuous wood covers with a cad-controlled laser, did a very nice job on 6 or 8 mm wood...

 

[thewildest]

Just browsing here, was curious about the answer... why wouldn’t you try a laser cutter? It will leave a minuscule mark. I don’t know if the burned wood could weaken the structure.

 

[thewildest]

Our shop sometimes used to cut continuous wood covers with a cad-controlled laser, did a very nice job on 6 or 8 mm wood...

Oupps, didn’t see this one, same as what Mike said

 

[BassHappy]

Yes. Now, I (or your machinist) can put some set in the teeth, if you like. Like PilotJones says, that will widen the kerf. On thin wall plug cutting saws like this, I usually don't. I prefer to relieve the walls, inside and out, by a few thousandths, just behind the tips of the teeth. For example, the tips of the teeth are 0.030" wide; 3.750" OD x 3.690" ID. About 0.100" back from the tips, the diameters go to 3.745" OD x 3.695" ID. Behind the teeth, the wall thickness of the shell is 0.020". This has the same purpose as setting the teeth: it keeps the wall of the saw from rubbing against the wood and heating up.

Also, I like to use fewer, larger teeth for saws like this. It helps to clear the chips out and keep it cooler, plus it makes it easier to resharpen. I'm thinking 24 teeth for this 3.75" saw, but maybe even 12 would be better. If necessary, I'll file the gullets (the notches between the teeth) extra deep to help clear the chips.

I also make the back relief of the teeth pretty shallow, as you can see on those cutters above. This limits how much each tooth can take per mouthful, so it doesn't dig in and rip up. I want a cutter like this to go slowly.

With a plug cutter of this size, I don't recommend backing up and trying to reinsert it. Unless you have it really tightly fixtured in a milling machine, there's too much chance of it kicking and chewing up edges of the cut ring. Bring it down to contact and push it quickly down to the full depth.

Did we mention that you need to put a clean piece of MDF underneath?

I'm assuming that the sequence is to cut the matching plug from a 1/4" thick sheet of gorgeous wood, which then gets glued onto the back of the body, positioning the hole over the cavity that's pre-routed in the body center wood.

Hey Bruce...

Here is what happened on the first go round last year with the Milwaukee hole saw I bought. We clamped the body down hard, and used the slowest speed on the drill press. I wasn't concerned about using these as grain matched covers, as I had some custom 3.75" covers I wanted to use. You can see how thick the groove is around the hole.

I then used a 3.5" hole saw to create the ledge for them to rest on:

But, the 3.75" covers were spot on measurement-wise but fit unacceptably loosely in the holes. We took a lot of care, but somehow, there was just too much shimmy in the hole saw/drill press process. We tried first as a test on a piece of MDF and it worked great and the covers fit fine, but not on the actual wood. Keith actually made some really nice walnut covers for me that are slightly oversized and fit snugly in the holes. However, I found a laser etching company in Canada, and they are making me some custom covers for these with a design on them. I sent them one of Keith's covers to use as a pattern for these yesterday.

The plan for the new ones - I will send them the actual covers once they are cut out. The exact size is moot, since they already fit - and they will do the custom etching and send them back. We are going back and forth on the etching but it's looking like a mandala I designed using an atomic theme. I like the idea that the industrial/modern meets the handcrafted wood thing. It's just part of my design philosophy that cavity covers deserve better. In a perfect world, they should become a part of the design not just a functional after thought. Just my opinion, I could be wrong.

The drop backs will start out at no more than 1/4" thick. I plan to cut all the way through with the new 3.75" hole saw. Then the laminate wood under it will have the 3.5" hole that will create the ledge. Then I will glue them up. They will be chambered so the backs in the center will end up around 3/8" thick once they are hogged out. I figure there will be 10 in this batch and it's worth automating the process a bit. I have seen some amazing stuff with small jeweler's saws and tiny scroll saw blades, but when you are paying shop time by the hour, you want to maximize your production bucks. Plus a hole saw as you describe should create a perfect circle and eliminate some of the guess work.

 

[Bruce Johnson]

One other thought about this:
Maybe it would be best to do this operation by hand; use the big thin wall custom hole saw in the drill press, but don't turn the motor on. Rotate the hole saw by hand, slowly, with gentle down pressure.

If you make up the hole saw as I described, with a 1" steel arbor, mill some flats on it, up about an inch or two from the saw shell. So there's a 3/4" (or whatever) square section midway up. Then the arbor reduces down to 1/2" diameter to go in the drill chuck. Clamp a 12" or 14" Tap Handle on the square section.

This is a Tap Handle, if you aren't familiar. They clamp on anything square, like a tap or a reamer. You can find them at flea markets for a few bucks, in all different sizes. I have a whole row of them, from 6" to 24". Very handy tools.

https://www.amazon.com/uxcell-Reame...1523134528&sr=8-13&keywords=tap+handle+wrench

Clamp the tap handle on the shank of the hole saw, and put the hole saw in the drill press chuck. Unplug the drill press to make sure that you can't accidently turn it on. Clamp the wood down on the drill press table, on top of a piece of MDF. Use the tap handle to gently press down and turn the saw into the wood. If it feels like the chips are jamming up, stop, raise the saw, brush out the teeth, reinsert and resume turning.

Assuming that the saw's teeth are reasonably sharp, it wouldn't take many revolutions to go down through 1/4" of wood. It's just a small hand saw going in a circle.

Going slowly, turning it by hand, and applying down pressure by hand, you can be sure that it's not going to skitter or jump out of the groove. And you are not going to burn the wood.

 

[BassHappy]

One other thought about this:
Maybe it would be best to do this operation by hand; use the big thin wall custom hole saw in the drill press, but don't turn the motor on. Rotate the hole saw by hand, slowly, with gentle down pressure.

If you make up the hole saw as I described, with a 1" steel arbor, mill some flats on it, up about an inch or two from the saw shell. So there's a 3/4" (or whatever) square section midway up. Then the arbor reduces down to 1/2" diameter to go in the drill chuck. Clamp a 12" or 14" Tap Handle on the square section.

This is a Tap Handle, if you aren't familiar. They clamp on anything square, like a tap or a reamer. You can find them at flea markets for a few bucks, in all different sizes. I have a whole row of them, from 6" to 24". Very handy tools.

https://www.amazon.com/uxcell-Reame...1523134528&sr=8-13&keywords=tap+handle+wrench

Clamp the tap handle on the shank of the hole saw, and put the hole saw in the drill press chuck. Unplug the drill press to make sure that you can't accidently turn it on. Clamp the wood down on the drill press table, on top of a piece of MDF. Use the tap handle to gently press down and turn the saw into the wood. If it feels like the chips are jamming up, stop, raise the saw, brush out the teeth, reinsert and resume turning.

Assuming that the saw's teeth are reasonably sharp, it wouldn't take many revolutions to go down through 1/4" of wood. It's just a small hand saw going in a circle.

Going slowly, turning it by hand, and applying down pressure by hand, you can be sure that it's not going to skitter or jump out of the groove. And you are not going to burn the wood.

Sounds like a great idea Bruce. I am sure once I had the tool I could do some experimenting on a few scraps of different woods - to see what works best. Good point about not burning the wood too.

And this comes from the Far East, so I wouldn't trust the quality of the steel, but I wonder about the concept and design of it, being a diamond cutter - again probably not thin enough:

Might make the rounds of Lennox and a couple other hole saw makers - they are already tooled up so maybe it wouldn't be a big deal for them to modify one for me.

 

[Bruce Johnson]

Don't use diamond-encrusted tools for cutting wood or most metals. Diamond tools are made for cutting stone, concrete, and glass.

It may be possible to take a section of bandsaw blade stock, curl it in a circle and weld it. But it would be tricky to get it formed into a nice circle. Probably not worth the trouble. I think it would be easier to just machine it from steel. Either from a solid slug, or a piece of steel tubing.

If you start with a standard 3 3/4" High Speed Steel (not Carbide tipped) hole saw, you could trim it down to a thinner wall thickness. It would be done by grinding it internally and externally with a Tool Post Grinder setup on a lathe. Your local sharpening shop may be able to do that. Or, your neighborhood machinist may have a Tool Post Grinder. Whether that would be less expensive than making your own custom saw from scratch, I couldn't say.

 

[BassHappy]

Don't use diamond-encrusted tools for cutting wood or most metals. Diamond tools are made for cutting stone, concrete, and glass.

It may be possible to take a section of bandsaw blade stock, curl it in a circle and weld it. But it would be tricky to get it formed into a nice circle. Probably not worth the trouble. I think it would be easier to just machine it from steel. Either from a solid slug, or a piece of steel tubing.

If you start with a standard 3 3/4" High Speed Steel (not Carbide tipped) hole saw, you could trim it down to a thinner wall thickness. It would be done by grinding it internally and externally with a Tool Post Grinder setup on a lathe. Your local sharpening shop may be able to do that. Or, your neighborhood machinist may have a Tool Post Grinder. Whether that would be less expensive than making your own custom saw from scratch, I couldn't say.

Hey Bruce

Thanks,

I have no problem having you build it but you seem reluctant with your limited amount of time these days. I haven't heard from my local guys yet, we will see what they have to say....