CNC Standard Bit Set - opinions requested (list edited 050916)

Woodshop
1

We’re planning on adopting a much reduced set of standard bits for the CNC router, which we keep stocked and maintained, and removing most of the oddball bits from the vCarve tool library and cabinet. The question remaining, is what bits to stock, that will meet user needs for most work? I’ve discussed this with Alex, Matt, Andrew, etc, but wanted to hear any other thoughts you might share. The objective, is to stock a maintanable set of bits, to keep costs low, so we can replace dull or broken bits and collets on a regular basis.

Normal materials we will address, include hardwood, softwood, plywood, MDF, laminated MDF, Acrylic, HDPE

Proposed Basic Set:

vCarving
60 degree vBit, 3/4 diameter x2
90 degree vBit, 3/4 diameter x2

Hardwoods/MDF
1/8 End mill upcut x1
1/4 end mill upcut x3
3/8 endmill upcut x1

Hardwoods/Softwoods
1/8 End Mill, downcut 2 flute x1
1/4 End Mill, downcut 2 flute x3

Plywood/Laminates
1/8 Compression, plunge tip x1
1/4 Compression, plunge tip x2
3/8 Compression 3 flute chipbreaker x1

Plastics (Acrylic, HDPE, Polycarbonate)
1/8 “O” bit, single flute (Plastic) x1
1/4 “O” bit, single flute x1

Various
1/8 Ballnose, 2 flute x1
1/4 Ballnose, 2 flute x1

Specialty
1/2" end mill (resharpened)

Collets

1/8" x2
1/4" x2
3/8" x1
1/2" x1

***List modified to reflect discussion

Thoughts and suggestions?

4 Likes
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Suggestion,
Don’t remove the bits from the V-Carve tool library. Instead I would suggest having some bits labeled as stocked and user supplied. To the best of my knowledge we are not hitting a limit to how many bits we can hold in the v-carve library, rather we are trying to save money by stocking a smaller amount. Plus, having a user supplied category of bits would allow other members to share the information they figure out for more specialized tooling.

I’m planning on figuring out some poly-carbonate tooling feeds and speed for Chuck Graff in the some what near future to do motorcycle windows. I’ll be purchasing my own tooling and I don’t mind sharing the info with the rest of the space once I’ve figured it out. This would be a good place to share that info for others to use later if they wanted to buy the same tooling.

As for 3/8 bit I see what your getting at. I’ve found the 3/8 bit to be much faster than the 1/4. But if I need the speed I’d probably be willing to purchase my own bit.

Forgot to add, Thanks for taking the time to do this.

5 Likes
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If there is a limit, we might painfully discover it once we add all of those duplicates for all the different materials :slight_smile:

1 Like
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We’re not too worried about a library limit, rather, we want to 1. Be able to stock affordably 2. Keep it simple for training and operational purposes 3. Add plastic 4. Fix a number of operational issues we’re observing.

As for user supplied bits, there’s not really any rules or policy about it, though it’s been discouraged generally. What we’re observing, is that even experienced users are getting their feed rates wrong more often than not - so setting up the library to work for 95% of jobs, with a solid F&S settings is one of the goals here.

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I don’t think downcuts need to be part of the standard library. If you need downcut, it should be used finish pass only to prevent a large cake buildup in the annulus.

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@Tapper, that looks like a fine list of standard bits to me and I agree with the idea of the Space supplying only those basic bits.

However, we need to be tolerant of user-supplied bits. That’s a good set of basic bits for most applications, but there are some things that they can’t reasonably do, like a standard roundover edge profile…

I have projects coming up which require a metric crap-ton of roundover profiles. They will be fast and easy if I supply my own roundover bit, but I don’t want to offend the woodshop gods.

Users may make initial mistakes in setting their feed and speeds, but they have strong motivation to fix those mistakes to protect their expensive personal bits from damage.

1 Like
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I’m not against user bits personally, but it’s really a subject for another discussion. Really wanting discussion about the bit selection posted above right now.

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I think the reason downcuts are here, is because of the vacuum holddown - upcuts can be a real problem for smaller pieces of stock. Likewise, upcuts sometimes leave undesireable surface defects. Downcuts do the same on the bottom surface, but I believe Alex is teaching people to onionskin their cuts, so the downcuts seems a better fit, though I understand the point youre making about dust evacuation and heat.

1 Like
9

you left out the 1/2 inch bit.

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That’s what tabs and other hold down methods are for. In the machine shop, you’re responsible for fixturing your work… Why’s it different here? The vacuum table is one tool of many for holding down work.

The downcut builds up dust in the annulus, regardless of how effective the dust collection is, which the spindle has to work harder to get though when it comes back around on a multi pass cut. Additionally, you end up unevenly wearing the bit because you’re only cutting on the first 0.125 (or whatever the pass depth is) and then sanding the rest of the engaged cutting edge as you break up the cake.

The surface finish argument is moot when you use it multi pass anyways, it rubs the cut surface each pass as it goes down.

1 Like
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Problem is, especially on hardwood, that first pass causes a lot of tear out in the surface, so for hardwood, I’ve never been able to get a clean cut with an upcut bit. All that being said, I wouldn’t oppose upcuts, but I added them as downcuts, because that seems to be the consensus atm.

Say what? Don’t think our gantry will even run fast enough to drive a half inch mill at chipload!

1 Like
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Which is why downcut bits are a specialty tool for final passes after a rough out.[quote=“MathewBusby, post:5, topic:9237, full:true”]
I don’t think downcuts need to be part of the standard library. If you need downcut, it should be used finish pass only to prevent a large cake buildup in the annulus.
[/quote]

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am i missing something, theres 1/2" mills in there now i use them all the time? Should be 2 of em in there in fact.

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I use the .5 and .375 all the time don’t remove those

1 Like
15

Which ones? Normal end mills? I think you’d find that a smaller bit would do the job if it was running at its designed rates. They’re currently tuned waaaaaaay down.

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I’m cutting 11 5x8 1.4 deep pockets in yellow pine each run.

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yes, do not remove the .5" endmill it does get used, and cuts fine at the current rates in vcarve.

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Gets us back to goal number 1 - reducing the cost of maintaining our bit selection. The problem with those big bits, is that they are more expensive in comparison to the 1/4" bit. The 1/4 can cut any job the 1/2 can cut, albeit a little slower, and the 1/2 is used by only a few souls. How much should we increase the cost of our basic stock of bits to accomodate relatively rarely used bits? Don’t forget the extra collets needed as well (our collets are also worn out).

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I guess my argument is those that use the CNC ALOT, use those .5 bits to cut deep pockets as clean out. We will go through through those 1/4 bits like nothing. I think its a tradeoff and your talking about adding on a possible 40 mins to an hour per tool path with a smaller bit for those large cleanout jobs.

I’ll go with whatever you decide Tap as you are more versed in this stuff than I am, but that bit will be missed by the frequent super users of the CNC.

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← Not the decider, just trying to herd the issue towards action. Our bit supply is generally dull, and many of the collets are worn out as well. We need to buy more, but its a big $$ order, and needs to correspond to an update of the vCarve tool lib as well. Alex, Matt, Kent and others have been talking about this for a while, but I don’t think a perfect consensus is possible, so just want to at least implement as much as possible, to get the ball rolling.

With respect to upcut vs downcut, the downcuts are clearly better on hardwood, but upcuts are clearly better for MDF. Probably more MDF gets cut by some margin. Maybe we could just sharpen the half inch bits, and adjust the tool lib to the new dimension, so that we can afford them.

Going to modify the first post to reflect some of this.