Violin Forum/Message Board

Barry Dudley · Member Joined: 01 Jan 2008 Posts: 64 Location: Monroe, GA

I cannot seem to find a "downcut" spiral bit from McMaster Carr or MSC. I find the "upcut" size to use in my Foredom tool but not the "downcut" bit.

StewMac has them but they are twice what I have paid at McMaster Carr or MSC.

Can anyone help with a source or part #?

Andres Sender · Posted: Thu Jul 17, 2008 1:18 pm Post subject:

FWIW none of us use downcut, not Michael D., not Coen, not Craig Tucker, nobody but the guitar people and the occasional violin maker who presumably can work with the restricted sizes, as far as I know.

Michael Darnton · Posted: Thu Jul 17, 2008 1:44 pm Post subject:

Because they push chips down into a closed hole, they tend to break more often when used for purfling. On guitars, where the cutting is usually open-sided to give room for the chips to clear, this isn't a problem.

David Tseng · Posted: Fri Jul 18, 2008 10:01 pm Post subject:

What is downcut or upcut? Is the difference in the left or right hand thread? Is normal drill bits upcut or downcut?

Andres Sender · Posted: Fri Jul 18, 2008 10:27 pm Post subject:

Normal drills and mills are upcut--they remove waste upwards out of the cut, and yes the difference is the handedness of the flutes.

[edit--Chris--and then I stole the last bit of your thunder by adding the bit about flutes before I saw you there! Razz

]

Chris Knowlton · Posted: Fri Jul 18, 2008 10:28 pm Post subject:

Sorry Andres we posted at the same time.

It depends on the direction of the flutes. A standard drill bit is an example of an "up-cut" bit. The spiral flutes bring the waste wood up and out of the hole. A "down-cut bit typically leaves a cleaner edge because it shears the wood fibers by directing them down whereas an "up cut" bit can lift the wood fibers around the hole or channel depending on the type of wood and on how sharp or dull the tool is and how fast it is spinning.
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Chris Knowlton · Posted: Fri Jul 18, 2008 10:41 pm Post subject:

FWIW My first attempt at cutting a purfling channel using a drill press and an up-cut bit did not end well. When repositioning my hands I reduced the "hold down" pressure on the plate. The spiral of the bit lifted the plate and the bit cut completely through the plate. Higher bit speed would probably have helped. I went to a down-cut bit and had no problem. Luckily the plate I destroyed was my "practice" plate.

BTW The up-cut bit cut cleanly and works well as long as you hold the plate down.
_________________
I make sawdust mostly

mikemolnar · Member Joined: 30 Mar 2007 Posts: 57

Darnton is on the money about downcut end mills. My experience is that they are not appropriate for cutting a narrow channel as the chips compact and build up.

I used to put down a coat of sealer (shellac or egg white) before running the Dremel with a regular upcut end mill. This eliminated the frizzies. But I found that simply running a folded piece of 320 sandpaper along the channel cleaned up those frizzies. I now do the latter.

These notes are from I "Segreti" Di Molnari. (Big Grins)