Time to select bits for 3D cutting.

[brian_h]

I haven't done any cutting yet on my new shopbot, mainly because all I have around the shop is 1/4" spiral up-cut bits and the shopbot will be cutting larger, 3D forms out of wood.

Can I check with you guys before I start spending money?...

I'm going to be shaping hardwood 4" thick (Z) into rough 3D shapes (no fine detail but lots of curves on the z axis). Am I right to assume I should get something like a 1/2" ball nose end mill? I probably should get a 1/4" too, just in case. Is this right??? Anything else I should consider????

[billp]

Brian,
It wouldn't be a bad idea to have a few long (3"), by .5" bits around either as some software packages let you do a roughing pass based on "Z levels". It's sometimes faster to go in and rough out a 3D shape with a flat bottomed bit, and then come back with a much smaller, ball nosed bit for further detailing. In these cases the software will let you determine just how much of a "safe factor" you want to leave in your roughing pass (for example you could tell it to leave at least .2" beyond the final shape you want to actually carve. This insures that the roughing toolpath will not encroach into your final product...).
You could then decide (based on the thickness, and density of your wood) how deep to make each of these "Z level passes"...

[thecustomsignshop]

The 3" by 1/8 bit is excellent for finishing work, we use them all the time. What software are you using for 3d Brian?

[brian_h]

Rhino/MillWizard

I also own Bobcad v18 & v19, but I don't plan on using it for this.

[frank_hav]

I try to use the biggest endmill/ballmill I can for 2 reasons.

1) Strength
2) Cusp height related to pick size.
see the attatched sheet

Cusp Height pdf
Cusp Height Chart.pdf (http://www.talkshopbot.com/forum/messages/312/Cusp_Height_Chart-14904.pdf) (13.3 k)

[mziegler]

Frank, also a larger bit will have a faster production time and give the part a better finish. This might be contra intuition, but a larger bit will have smoother finish then a small bit. The cusp height is the main factor that determined the smoothness of the surface. Mark

[brian_h]

I learned a new term today, "Cusp". Thank you Frank. I didn't know the term for those lines.

"Cusps, those linear ridges running along the tool path, are the telltale surface characteristic left behind by a milling operation with a radiused cutter."

"Pick size"- I'm not sure I know what that means. I'm guessing it's the diameter of the ball mill. Anyway, I get the idea. This is very relevant for me. I would gladly trade additional machining time for a better finish. I'm short on available hand-work time. The larger bit allows me a larger step-over while giving a smaller cusp height.

Bill brings up a good point about using a flat-bottom bit for roughing. I wonder if there is a cost factor in this decision. Do flat bits save enough to make up for the bit change? Or would it be better to rough and finish the shape with the same .5 ball mill? I don't think these shapes will need more detail than what a .5 mill will produce.

BTW- Frank, I played guitar in bands for many years and totally appreciate where you work. Nice!

[brian_h]

...and, Frank, thank you very much for the cusp height chart. That looks very helpful.

[frank_hav]

Brain,

Pick size is the same as the radial stepover in the chart. Basically it's how far the stepover is from pass to pass.

Glad you can use the chart. Metal doesn't sand as easy as wood so I always use it all the time to control my handworking time.

And yes Community rocks. It is a very fun place to work, and they're convinced I parted the Red Sea many years ago. Love'em Great place.

Frank

[brian_h]

Frank...

...please think of me if you ever have to "throw away" a floor monitor or two (slim chance). I'm trying to get my kids interested in music and I regret everything I got rid of when I stopped playing on stage.

Someday I'll probably try using the shopbot to build a solid-body electric. A new LesPaul is $4K, and there's not much chance that's going to happen.

[brian_h]

My bit supplier does wood bits and doesn't sell "ball mill" bits. She does sell "core box cutters", which has the radius on the bottom but not much blade on the shaft. I got two bits to try out, but I'm very uncertain about if this was a good choice.

So, it looks like I need another bit supplier. I'll dig through the posts later tonight when there's more time to spend. If you have a good supplier for ball-end mill bits, please share.

[frank_hav]

Brian,

Ballnose cutters are everywhere on the net.

I use Onsrud solid carbide router bits. Ask them for a book. Great info inside about cutters and such inside. Also when your shopping you have the part number your looking for. When I need it quick MSC carries some and can get all.

In general you will be looking for router bits not endmills when cutting nonmetalic materials.

Router bits are ground differently then endmills. They are made to cut wood and such. Endmills that are ground for Aluminum work somewhere in between. You will learn what you get and what you can get away with as time goes on.

Both router and milling bits can be resharped generally. Use SHARP bits, save the old ones, and have them resharpened. Resharpened bits work fine just remember to adjust tool sizes. After a few sharpenings the will not perform as well due to chip clearance isssues. You can decide when or a good tool-grinder will tell you when he looks at them.

Get the book even if you never get a cutter from them.

Monitor? We used to be able to take rejected speakers until a resently ex-employee decided they were going to sell them on ebay. Now we destroy every rejected part.

As a general note asking about cutter brands is about the same as asking what tastes better Coke or Pepsi. I along with everyone else will have there favorites.

Frank

[brian_h]

These are the two bits I got to try out. What do you think about this style of bit to do 3D work in wood? This will be my firt time doing 3D cuts and I'm feeling a little uncertain about bit choice. Last night I found it was easy to find rounded end mills for metal, but nothing specifically for wood. Last time I tried using a metal bit for wood (2D) the cut was really bad. I'm afraid of wasting time and money on a stupid bit choice, and ending up back where I started.
6622

[steve4460]

Hi Brian

Check out this bit sellection.
http://www.shopbottools.com/spindles.htm

[paco]

Brian,

those will be perfect but this size will be for roughing. Ask for 1/4"-1/8" (I have those in carbide tipped) and even 1/16" if possible. For the latest, you may have to look at specialty but this such small size will be only useful for very intricate carving. You shouldn't have too much problem finding solid carbide spiral up ball end; Onsrud, most generics, metal tooling...

BTW, the above bits will perform much better than SC (solid carbide) spiral up on profiling task and are WAY more affordable than solid carbide. They have shorter length (both cutting edges and shank) thus provide a more balance tool on heavy load.

When you'll get into steep and deep 3D carving, you'll want to check for extended shank length.

[patricktoomey]

Brian, I use the same style bits frequently for 3D carving in both wood and Corian. I typically use 1/16" up to 1" bits at different stages of the carving. I've been very happy with the results. These bits are expecially good for carving columns with an indexer.