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i just recently spent sime time modifying an old duplicarver to fit guitar tops, and i was wondering what type of bit would work best. My guide pin is a half inch steel rod, so i was planning to use a half inch straight bit, but I'm not even sure if a straight bit is what I should be using. I thought that i would try to find a triple fluted bit and that maybe that would work better. any suggestions?

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~shad peters

http://www.flickr.com/photos/petersinstruments/
http://petersinstruments.blogspot.com/
http://petersinstruments.com/

Never used a duplicarver and I'm still waiting on my CNC machine but I would think that a ball nose bits and followers would be the way to go. You could get a set of 1/2", 1/4" and 1/8". As to followers, that might be a bit more complicated to source but, you might be able to find someone to machine it for not too much.

I think that for wood, two flute spiral is probably the way to go.

One other thing you might consider is making the router mount so that in addition to mounting perpendicular to the surface, you can mount it at a slight angle like 10 degrees. This puts a faster moving part of the bit in contact with the surface. To be safe, you'd need to have your follower adjustable in the same manner. This would only be with the ball nose bit of course.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Shad,

Could you be more specific when describing what you are going to use the carver for? I can't visualize "fitting" a top with a carver.

I have hundreds of hrs of experience running duplicators (pantographs) from single spindle machines all the way to six spindle. The machines I owned were used for rifle stock and pistol grip production and all of them ran up to 20 hr days with three operators.

Some photos of your machine and set up would help.

Mike

Mike I am not sure why I used the term "fit" (sometimes i confuse even myself) but what I am really doing is rough carving arch tops.

Here is my basic setup, its very simple. The bones are from an old craftsmen unit, I just made it bigger. I'm planning to loose the pulley wheels on the side here very soon and install some linear bearings.

_________________
~shad peters

http://www.flickr.com/photos/petersinstruments/
http://petersinstruments.blogspot.com/
http://petersinstruments.com/

Shad that is exactly what I started out on and did the same thing on conversion, except I made mine 60" long! I also did not use the table but used indexable centers.

For your bit use a common 2 flute carbide tipped flat bottom cutter and when you set your work up leave about 1/8" gap under the bit until you know what kind of flex you are going to have....because you are going to have flex!

If I can be of service, just holler!

Mike

While a straight bit can remove alot of material, if the surface you are carving (archtop, mandolin, solid body) is arched or hollow, it is easier to use a round core box bit as it will cut closer to the profile of the curve although it will tend to cut less aggressively than a straight bit. I have a Marlin Duplicarver and use a 1/2 round tip stylus with a 1/2 core box bit. The core box bit has a 1 inch length so it can do the same side cutting as a straight bit.

I already did a test run and noticed some flex, I cant imagine the flex you would get on one that was 60" long! were you still using just 5/8" rod?

_________________
~shad peters

http://www.flickr.com/photos/petersinstruments/
http://petersinstruments.blogspot.com/
http://petersinstruments.com/

My machine was the same width between stylus and cutter as you hve, but the rails were much longer.

I would like to encourage you to take a look at putting your extra money into a cnc instead of upgrading this carver. I spent a small fortune on "tinkering" with machines and once I carved my first cnc carve, all the manual machines went away. I don't have to worry about getting tired, I don't have to worry nearly as much about lost parts due to tearing out as I did with the manual machines.

Shawn is correct about the core box being able to carve closer to the finished surface, but you did say rough carve. I might add that an experienced operator will most of the time prefer the flat end cutter for everything except the final finish, and my guys would then put a very slight radius on some of the flat end cutter bits to make a quasi core box. With the flex you have in your machine, I don't think you will be able to carve a finish carve anyway, but, you won't know till you try.

Mike

right now I am not really wanting to get to involved with cnc, i really dont know anything about how to program one or what all it will take to do so. i know very little about them but at the very least i am sure i will need motors to power the front-back
left-right, and up-down motions, plus threaded rods and whatever programs I need. I might look into it in the future, but right now I just don't have the time or money to invest into it. the only reason i have invested time in this project is because i have essentially gotten it all for free, I was even able to get the linear bearings i was talking about upgrading to at no cost. otherwise i would not be upgrading this carver.

_________________
~shad peters

http://www.flickr.com/photos/petersinstruments/
http://petersinstruments.blogspot.com/
http://petersinstruments.com/

[quote="
One other thing you might consider is making the router mount so that in addition to mounting perpendicular to the surface, you can mount it at a slight angle like 10 degrees. This puts a faster moving part of the bit in contact with the surface. To be safe, you'd need to have your follower adjustable in the same manner. This would only be with the ball nose bit of course.[/quote]

That makes a lot of sense to me as the "zero RPM" or cutting speed at the center of the bit will tend to compress wood fibers rather than cut them.
Nelson

In the interest of full disclosure, that idea was based on a comment Brad Way made that it's common on 5-axis machines to do exactly that for the reason you mention.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Andy, that's interesting because several years back I was considering making a mount for my router motor so that it could be tilted slightly for that reason. I was getting a lot of fibre crushing at the center especially when cutting spruce with a 3/4" diameter ball nose. I've am now using the Nova cutter system with two replaceable carbide blades that overlap center in a way that the tool cuts rather than "bulldozing" the center area. It's available with 1/2" and 1" diameter ballnose blades with 1/2" shank diameter. http://www.amanatool.com/bits-fv/ns-100.html
The blades are a little tricky to install into the cutter until a person "gets the hang of it". The carbide is sharpened with a very sharp relief angle but it's amazing how well they stay sharp even in production cutting of maple for archtop plates.
By the way, Brad Way is pretty sharp also. (Bit of a pun or something there, I guess)
Nelson

That makes a lot of sense to me as the "zero RPM" or cutting speed at the center of the bit will tend to compress wood fibers rather than cut them.
Nelson[/quote]


Nelson the zero rpm thing is exactly why I suggested the two flute carbide tipped router bit. When carving the gunstocks and pistol grips I could get a much smoother surface with the two flute flat end cutters than I could with ball nose cutters. In addition, when carving close to net shape, sanding the tool path out of a piece carved with a ball nose is much more difficult than one cut with sharp edges.

I noticed your last post about the insert bit. I will have to take a look at those. Thanks for the link.

Mike

http://www.toolstoday.com/p-5124-plunge-type-routing-body-for-12-inch-shank.aspx
http://www.toolstoday.com/p-5127-plunge-type-routing-knives-core-box.aspx

Mike, the first url above is for the cutter body with 1/2" shank and the second url is for the replaceable carbide inserts.
Below is a link to a previous discussion on cutting tools:

http://www.luthiersforum.com/forum/viewtopic.php?f=10106&t=24586&p=336253&hilit=+nova#p336253

Be safe everyone!

Nelson