Hole saws - what size do they actually cut?

[SolarYellow]

I went through my hole saw set and did test cuts in some inexpensive plywood just to see what size they actually cut.
Questions:
1. Are any of the saws I have useful for rocketry?
2. Would it be likely to be worth buying any other sizes on account of their usefulness in rocketry.

The answer to the first question is, exactly one. The 2 1/8 saw cut a 1.93# plug, which fits perfectly in the ID of Estes 2-inch tubing. And it did it again in 1/2-inch MDF. But that's still less useful than fitting inside a coupler.

Every other size is too far off available tubing ID or OD to be a useful fit, IMO. Several are close, but will require additional sanding or tuning up on a lathe. Sanding is problematic in that it is liable to lead to roundness and/or concentricity issues if significant material is removed. Messing with them on a lathe is perfectly nice if you have that resource, but it's still more steps than I am looking to do to make this work.

The answer to the second question is, probably not. The variability in how each saw cuts means it's a roll of the dice. If you buy a saw, the only way to know what size it will cut is to make some test cuts. And then you own it, whether it's useful to you or not.

I did not make repeated cuts, and I didn't try different materials. It was really cheap 1/4-inch plywood that I have no other use for. The one exception to this is the 2 1/8, which I did in two different materials. It was within a few thousandths, with a similar fit of the bulkhead in the body tube, in both materials.

In a world where CNC routers and laser cutters are increasingly available, I think I'll leave the hole saws on the shelf.

 

[tsmith1315]

I use hole saws as a starting point for rings in sizes that are close enough. Finish up the OD with a disc sander and the ID with a drum.

It’s not for everyone, but I find hand working materials much more enjoyable than button pushing.

 

[MClark]

I use the fly cutter type.
Have several so I don’t have to adjust for sizes.

https://www.homedepot.com/p/MIBRO-A...GLtOOQXnq5TmtjRJMzhoCzmYQAvD_BwE&gclsrc=aw.ds

 

[SolarYellow]

If you're going that route, HF has the two-cutter variant for around half of what I've seen it for anywhere else:

https://www.harborfreight.com/carbide-tip-adjustable-circle-cutter-68117.html

 

[RokitFlyr]

I've been using them for years. The size refers to the "hole". What we are typically after is the disc left over. Just subtract the curf from the size of the saw. This can vary greatly depending on the type of saw. A little sanding is no big deal. So a 2" disc would require a 2 1/8" holesaw.

 

[FredA]

Sure I'd use a CNC if I had one for this, but for those without I've found the best way to make round things is to use a circle jig on a router.
Nice bonus is that you can cut stepped OD's so you can make nice 3D caps to make coupler closures similar to what you get when you laminate two different sizes of FG as some kits offer.
You can also cut stepped ID's to do things like capture motor mounts and such.

Plus - when doing large circles - it's a million times less scary than a fly cutter.

Also - buy a bit that pulls chips upwards - better edges

 

[lakeroadster]

I rough cut the disc with the hole saw, then use my wood lathe to clean the part to the finished size, typically for Centering Rings.

But the double fly cutter is nice.. I use one of those also.

 

[techrat]

Yes, for those of us that don't have mega-buck laser cutters, you're NEVER going to get an exact cut with an analog tool. I use a harborfreight circle cutter that fits into my drill, and if I'm within 1/4" either way, close enough, I either sand off the difference or push the bulkhead further up the nosecone. I try and think these things through of course, as I already have an idea of how rough it's going to be and for most of my rockets, tolerances are not that critical.

 

[MidOH]

Cause wood lathes are too hard to come buy?

 

[SolarYellow]

Cause wood lathes are too hard to come buy?

Some of us have limited shop space. Wood lathes generally take up a bit of room. They're also generally a manual process, requiring a lot of iterative checking, going a little more, checking, etc.

 

[MidOH]

Get a wimpy lil one from harbor freight. Fits in the corner of my basement.

If you toss the treadmill, and put it there, the wife won't even notice it.

 

[JohnCoker]

There are also Forstner bits, but they only work for holes. The good news is that they come in finer increments, such as 1/16" and they also produce very clean holes if used on a drill press.

 

[lr64]

I remember an article which I think was in the Whole Earth Catalog. It advocated wearing a big city telephone book on your chest when using a fly cutter.

Also, it's possible to make a faceplate lathe from a washing machine motor. Might still want that phone book.

 

[Bruiser]

Cause wood lathes are too hard to come buy?

Not if you have 600 plus to spend... Been looking for a fairly priced used one for a long time

-Bob

 

[lr64]

Not if you have 600 plus to spend... Been looking for a fairly priced used one for a long time

-Bob

In my town, and in another a few miles away, there are used tool stores which sometimes have things like that at reasonable prices.

 

[Blast it Tom!]

Err, them double fly cutters... how do they keep them in synch? Surely you don't manually adjust each cutter and hope they're both at the same radius? I have the single cutter version, and the "out of balance" condition is noticeable, so i don't recommend that one for precision work.

 

[SolarYellow]

Err, them double fly cutters... how do they keep them in synch? Surely you don't manually adjust each cutter and hope they're both at the same radius? I have the single cutter version, and the "out of balance" condition is noticeable, so i don't recommend that one for precision work.

Set up one to cut the OD and one to cut the ID of the centering ring. That will reduce the overall imbalance compared to having just one.

 

[rharshberger]

Set up one to cut the OD and one to cut the ID of the centering ring. That will reduce the overall imbalance compared to having just one.

Or just have several single cutter types like the General brand, once set and KEPT sharp they are very precise, also fly cutters shouldn't be run at a high rpm, follow the manufactures directions. The double cutter ones are not my favorites though I do have one. I occasionally use my flycutters now but for the most part I use 3D printed router guides. Tack the guide to a piece of material (usually wood in my case), rough outer radius on bandsaw or scroll saw drill center with a suitable size drill bit (usually forstner) then finish on router table...it took longer to type this than it does to make a ring using the router table and fit is near perfect first time.

 

[SolarYellow]

Or just have several single cutter types like the General brand, once set and KEPT sharp they are very precise, also fly cutters shouldn't be run at a high rpm, follow the manufactures directions. The double cutter ones are not my favorites though I do have one. I occasionally use my flycutters now but for the most part I use 3D printed router guides. Tack the guide to a piece of material (usually wood in my case), rough outer radius on bandsaw or scroll saw drill center with a suitable size drill bit (usually forstner) then finish on router table...it took longer to type this than it does to make a ring using the router table and fit is near perfect first time.

I like that.

 

[Steve Shannon]

When I got started, every time I got a new centering ring size that I thought I might like to duplicate someday I used my router table and a template bit to make a copy of the original centering ring in mdf. Then, when I needed an additional one I would use the template to mark it on the material I wanted, cut it out using a jig saw, and then use the template and the template bit to trim the edges. Double sided tape keeps the template and the CR material tightly together.

A note about vibration coming from a single bit fly cutter. If you’re getting vibration you’re turning it too fast. Turn it to a very slow speed and just let the drill press do the work.

 

[rharshberger]

When I got started, every time I got a new centering ring size that I thought I might like to duplicate someday I used my router table and a template bit to make a copy of the original centering ring in mdf. Then, when I needed an additional one I would use the template to mark it on the material I wanted, cut it out using a jig saw, and then use the template and the template bit to trim the edges. Double sided tape keeps the template and the CR material tightly together.

A note about vibration coming from a single bit fly cutter. If you’re getting vibration you’re turning it too fast. Turn it to a very slow speed and just let the drill press do the work.

And keep the cutter sharp!