How do I cut the profile on a 1 3/4” thick guitar body? What bits do I need? Thank you, Total Newbie.
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I use a 1/2" Compression bit, works real good for me.
Pat
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Thanks for the response, Pat. Is that 1/2” long compression bit or perhaps one with a 1/2” shank? I’ve never understood how my 1/4” Makita could use a bit with a 1/2” shank.
Mark
Thanks for sending the links, always good to see how others approach a project.
Mark
Sorry, I thought you had a spindle, yes it is a 1/2" shank bit, although I don’t see why a 1/4" bit wouldn’t work even with the extra long length of cut using conservative speeds and feeds as well as shallow depth of cuts
Pat
Pat,
Thanks for clearing that up, I’ve wondered how to use 1/2" shank bits for CNC–guess you need a spindle router. I will be cutting 1 3/4" hardwood; how long should the up cut/down cut/compression bit be? I’ve seen a bit at Bits and Bits that had a cutting length of 2". Would that be surdy enough to do the trick considering it has a 1/4" shank?
Thanks again.
Mark
Hey Mark,
milling bits are being deflected by the load. Therefore it is a rule to always use the bit with the shortest cutting part possible (and the shortest shank required also). A long bit for deep pockets is sometimes required, but should not be used as general purpose bit. People who have done this have reported problems with inaccuracies.
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Mark,
You can ask a dozen people for feeds and speeds and get a dozen different answers, if I was cutting what you are cutting I would use an up cut bit, 2 flute, about 50 IPM at 18,000 RPM with a depth of cut of .125 or so per pass, being you are using a 1/4" bit I would not recommend a compression bit in order to aid in chip removal, pretty deep for a 1/4" bit.
I am assuming you have the BB control and not the Masso so you cannot adjust the feed rate on the fly but you can vary the RPM.
There are no correct numbers for this, I tend to adjust mine to a good sound (hard to quantify) and the least vibration.
Hope this helps.
Pat
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Hey Mark,
in the video I linked above, which shows how to cut out a Jazz Bass solid body and then how to make a Jazz Bass neck with a CNC, they show all the bits used and they give the necessary cutting parameters:
If you read the “more” link you also find a link with a downloadable description.
Regarding the length of the bit (additionally to what I said about general bit length above), here if you cut from two sides, you need a bit with a cutting part that is only half the body height of your guitar body workpiece. So if you say your workpiece/body is 45 mm thick (1.75 inches), you would take a bit with 23 mm long cutting part (0.875 inches). So if you say you can only use 6.35 mm shank bits and not thicker, it would be an advantage to be able to use the short length / general purpose bit as you avoid unnecessary deflection or bit breakage danger.
Only if you want to cut only from one side, you would need a bit with a cutting part of the full height of your body. In this case you would need a long bit. 50 mm (2 inches) cutting part on a 6.35 mm bit, that’s rather long on a thin bit, I would expect deflection and be careful with the feed, as a thin long bit can break more easily.
The bits shown above are 8 mm (approx 0.325 inches) shank bits and as you can see this works well, no need for half-inch shanks. But by cutting from two sides, they avoid cutting the hole body depth which would require an extra long bit.
Makita routers are available with 6 and 8 mm collets everywhere (except in the USA where they have imperial collets).
If you want to use half-inch shanks (12.7 mm), you would need a milling motor with an ER-20 collet (can take up to 13 mm collets)
If you are a beginner, please be aware that finding the right cutting parameters can be done by trial and error, but usually it is much faster and leads to better results more quickly if you rely on professional education information.
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Hey Mark, hey Pat, hey all,
that’s considerably less feed than the suggestion in the video (5000 mm/min = approx. 200 IPM which takes an 8 mm bit (0.325")) and what you suggest Pat seems more appropriate considering the longer, thinner bit you plan to use Mark, and the DOC is similar (2.5 mm = approx 0.1" in the video).
Like I said if you ask 12 people you get 12 different answers, I only offer a suggestion based on my experiences.
Pat
Hey Pat,
I did not say something different than you, I agreed to what you said 
(edited my post by adding names to make it more clear)
I guess I misunderstood, sorry about that, I thought 200 IPM was way too much and good for breaking bits.
Thanks Aiph5u
pat
Thanks so much to everyone for your suggestions. I have heard about the Onefinity community and their willingness to help those of us who are new to CNC. You have proved the rumors correct. Thanks, Mark
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