Experts - How do I fix this? AZTEC CALENDAR

[bill south]

Hey Guys and Gals;
I've just started routing the aztec calendar and am having a bit of a difficulty. My first problem is my material. I'm using the costly but cheaply made birch plywood from Lowes (woes) and it is causing some hate and discontent here in the shop.
My setup is 24" x 24" blank using a 9/16 v-bit set for 100 ipm. I'm getting chipping in the design, and I would love to repair this after the 3+ hour run.
I'm thinkingof trying to fill the pit with (?) epoxy and re-routing the damaged area. My questions is, what is the best material to repair this with??? Ideally it will somewhat match the wood and be machineable. However, I'm up for any suggestions.
Thanks in advance.
Bill

[HuFlungDung]

Have you tried solid wood? Does the same sort of thing happen?

The trouble with (ply)wood is that it is not homogenous. I would suggest using something like MDF for the entire project.

[Parlorcity]

While I'm far from an expert in machining, perhaps all that's needed is a fresh perspective. What are your plans for the finished project? Do you intend to paint it? If so, many wood fillers (pencil type) use parafin wax as a base, and aren't paintable. On the other hand, if you were to take fine sawdust and blend it with some fillers and fill the affected area, your results may be acceptable.

Personally, I think that with a project with the detail that you're striving for, the plywood is the wrong medium, as it's weaker the shorter it's cut. Even if you're successful, it's only a matter of time till the wood dries and you've got cracking and separation of your hard work.

[louieatienza]

Cabinet grade plywood at the big box stores are not a good option. They normally contain voids and pockets, and areas that will chip off like you've found out. If you buy the pre-cut 2 x 4 sheets then it's pretty costly; buying a full sheet and having it cut there is the more economical choice.

If it were me, I would re-cut the piece. It may be fine if you use wood or filler, but who knows what area would fall off next, expecially when you start finishing it?

The best quality plywood you can use that is readily available is Baltic birch or equivalent. It is guaranteed not to have voids. There are different grades, mainly regarding the surface finish (some have patches, others do not.) There are also more veneer layers, so it is generally stronger. This is, however, IF you really need to use plywood. A softer hardwood like basswood, or alder, might be a better choice, and really not that expensive.

[bill south]

Thanks Louie;
I did manage to repair that calendar with a wood filler and painted it. It was for myself so I'm not worried about it falling apart. Heck, I've cut 20 or so since then and most have turned out nice. I'm going to start researching different woods when the weather warms up if it ever does!
Thanks again.
Bill

[Joe Crumley]

Bill,

This a drop dead beautiful file. It deserves better materials than plywood. For not much money you could go with 1" MDF. That stuff machines beaufully and can be finished in many attractive styles. HDU would also be a good choice but is expensive. I'd probably glue up some Alder.

Good to your work.

Joe Crumley
Norman Sign Company, Norman, Oklahoma, SandBlasted Signs, Sign Painter, Redwood Signs

[kolias]

Perhaps I'm wrong but a 9/16" bit is too big for such a delicate cut.

I would start with a 1/16" or even smaller

I would never use plywood

[Joe Crumley]

There must be some reason for using plywood but I can't figure it out. I also agree about the bit size. It seems much too large. Perhaps you could fill us in on your thoughts.

Joe

[kolias]

I’m new to CNC and experimenting to find the right bit size for intricate cuts as a hobby

I use 1/2" MDF for my experiments and so far the best bit for me is a 1/16” 60 deg V. which produces a sharp and clean cut. I have also ordered 1/32” single flute bits and I’m sure that they will produce good results.

I guess you can’t cut a corner lets say of 1/8” radius with a 1/2" bit. The Aztec design below has too many tight spots and it’s impossible to do a good cut with a 9/16” bit. Perhaps he meant 1/16”?

[Joe Crumley]

K.

Yep, I agree that must have been a typo. Still, I'm not sure about the plywood.

J.

[bill south]

Nope Guys;
I used a 9/16, 60° v-carve tool and used a v-carve tool path from Bobcad. I get some great detail with it! Regarding the use of birch plywood, I'm just a hobbiest and have been tuning up a new home made router. I use ply because it is cheap and doesn't bother me too very much to see it in the burn barrel. When I get my machine right, and get comfortable with repeatability, I'll switch to some better wood. I do cut some MDF but it dulls the tooling. Carbide bits are very expensive.
Thanks for all the advise. I really do appreciate it.
Bill

[bill south]

Hey Guys;
I thought I'd add a picture of a finished calendar. Not too bad for cheap plywood and some stain.
Bill