Official Luthiers Forum!

You can play the what-if's on bit sizes, stepovers, feeds & speeds etc with your software.

For example, a singlecut top with a 1" core box bit:



And with a .5" ball end carbide spiral for wood:



The core box bits are less expensive but shorter in length. The ball mill diameter is generally limited to the shank size and they are 2x the cost. I use them both where they work best.

Rand, I must be missing something, but I don't see how that tells you which cutter will work better. Can you elaborate?

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John Watkins
CNC Guitar Parts

So I'd like to ask a favor, do one of you have a top like the one that Rand shows that I could pull into Rhino and then play with Rhino Cam?? I *promise* I won't use for anything other than trying to learn the CAM software, this is the single hardest part for me to work through. I have some cheesy examples from the tutorial but I'dl like to try something a bit more complicated to see what it does with it. I'd also like to look at how you put it together...

If it's a problem then no big deal, I'm still stuggling my way through the tutorial on Rhino but want to play with the CAM software as well...

Thanks

-Paul-

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-Paul-

Patriot Guitars

Both cutters have the same profile, ball end, and in this case the part's features don't require the smaller diameter so the difference is amount of material to cut in a pass (runtime). In this case the what-if showed an 11 minute shorter program run by using the 1" core box bit for a similar finish quality. I'm sure these settings could be tweaked and the feed is rather low at 100 ipm for discussion purposes. A 2" core box is faster but the surface quality suffers a little. More meaningful when trying to figure out which tools are best for parts like necks where roughing and finishing are needed and trying to determine the best toolpath strategy to get all the part features. YMMV

Paul - I'll send a model to your email since I can't upload it here. <revised: got destination not valid error. email me at randkennedy at comcast dot net >

Rand Kennedy38862.4443865741

THATS TOTALY WICKED DUDE........

I was talking to a machinist today who mostly does metal but with some wood and he's found you're generally better off with the ball-end mills and keeping the feeds really high rather than getting a bigger cutter (big corebox) and using lower feeds.

The allure of a big core box bit is that it's essentially tangent to the cutting surface at any angle and thus you can have really shallow scalloping. The problem is that the cutting surface is moving at vastly different relative velocities depending on which part of the cutter is cutting and so you'd need to program toolpaths very cleverly to keep a consistent finish over the whole piece.

Right now it's looking like a Fadal for me (hooray for contacts). I know at Taylor, on their Fadals, they use either 1/2" or 1" solid ball-nose cutters to do their cutting. They've definitely put more time and money into this than anyone else.

Of course, you could get an ER-40 collet and use a 1" solid bit to get the advantage of the bigger cutter without the disadvantages of core box bits. Is there any other factor between a ball-nose and a core-box that I'm missing, Rand? From what I've been told, the core box has cutting geometry made for wood whereas mills are made specifically for metal and leave a rougher finish on wood. I can't seem to find core box bits anywhere with shanks bigger than 1/2", as well. The 2" one is from Amana, for CNC, and is only 1/2" but I'd feel better about using it over a 1" solid bit if it had a 1" shank.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Ok Bob if you get a Fadal I'm packing up here and moving in

Where are you guys getting your bits from? I'm going to be running mine on the 3-3/4HP Porter Cable router and will need to start collecting bits for it.

I found out yesterday that my machine is just about ready and will be here on the 19th next month so I'm getting excited, I'll definately have the shop ready for it by then.

-Paul-

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-Paul-

Patriot Guitars

I was looking at carbide.com and toolingontheweb.com. To find anything at Carbide.com I find it's easier to look the bit you want up on the Amana or Onsrud site and then do a search for the item number on carbide.com.

I've been told eBay is a good way to get bits if you can find them as they come really cheaply. A guy I know got 100 solid carbide 1/2" mills for $66, for example. I think that's less than the cost of the carbide used to make them.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

You folks are truly amazing!

Serge