What are the sturdiest bits?

Hi all,

For these open source machines, what bits would be considered the best? Anyone have any info on what I would need to cut relief in MDF, plywood cutting, ash hoop pine, alum, and acrylics/polycarbonates? I live on an island, where selection is quite limited, so it would be great to know what is best in America so I can buy while I am here.

THanks,
Chris

I started a thread on router bits and endmills, will post the link later when I get home....

That's a big list of materials, and what's best for one won't necessarily work as well for others. Also, "sturdiest" and "best" aren't always the same either. Carbide, for instance, stays sharp longer than High Speed Steel, but it's also more brittle, and can't be honed to as sharp an original edge. A 4-flute cutter is sturdier than a 2-flute, but you would usually go with 2 flutes for soft materials. If you're cutting contoured reliefs in all these materials, then a ball-nose tool would be required, although you can use flat or bull-nose cutters for roughing. And depending on the detail required, you'd need small cutters to get it on the finishing passes, but big tools for roughing, so it happens quicker. You might also look into tapered tooling, since it's more resistant to breakage than straight endmills, especially in the finer tip sizes.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

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Originally Posted by awerby

That's a big list of materials, and what's best for one won't necessarily work as well for others. Also, "sturdiest" and "best" aren't always the same either. Carbide, for instance, stays sharp longer than High Speed Steel, but it's also more brittle, and can't be honed to as sharp an original edge. A 4-flute cutter is sturdier than a 2-flute, but you would usually go with 2 flutes for soft materials. If you're cutting contoured reliefs in all these materials, then a ball-nose tool would be required, although you can use flat or bull-nose cutters for roughing. And depending on the detail required, you'd need small cutters to get it on the finishing passes, but big tools for roughing, so it happens quicker. You might also look into tapered tooling, since it's more resistant to breakage than straight endmills, especially in the finer tip sizes.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

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Thank you!,

That's a good bit of information. So what would be the best 3/8" bit for cutting patterns out of 1/2" plywood to get a smooth edge? Also, is there any particular company I should buy from?

Thanks for the advice.
Chris

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Originally Posted by Litemover

Thank you!,

That's a good bit of information. So what would be the best 3/8" bit for cutting patterns out of 1/2" plywood to get a smooth edge? Also, is there any particular company I should buy from?

Thanks for the advice.
Chris

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A 3/8" compression spiral would be your best bet. Vortex and Onsrud are two very good companies.

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Originally Posted by ger21

A 3/8" compression spiral would be your best bet. Vortex and Onsrud are two very good companies.

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Awesome thank you! I'll get one, or two. How long do they last?

Chris

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How long do they last?

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Somewhere between 4 hours and maybe 4 months. ;)

Tool life depends on many factors.
How many parts per sheet?
What material are you cutting?
Some plywoods can be particularly hard on bits. Some have very abrasive glues which will where grooves in the bits at the gluelines very quickly. Some will cause resins to build up on the bit's resulting in hotter running bits, which dull quickly.

To get the maximum tool life, you need to run at the highest chiploads you can. This keeps the bits cooler. Other than abrasiveness of material, heat is the main culprit in bits getting dull.
With harder plywoods like Baltic Birch, a chipbreaker compression spiral can allow higher feedrates, which in turn can give longer tool life.

Generally, if you're cutting 4x8 sheets, with maybe 6-10 parts per sheet, expect to cut between 20-100 sheets before the bits need sharpening. Cut quality will usually tell you when to change bits. If quality isn't that important, you can use a bit longer.

You can probably get a 3/4" bit sharpened 3-4 times. Sharpening will usually run around $20/bit, and each sharpening will remove around .015" from the diameter of the bit. So after 3-4 sharpenings, you'll basically have a 5/16" bit.

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Originally Posted by ger21

Somewhere between 4 hours and maybe 4 months. ;)

Tool life depends on many factors.
How many parts per sheet?
What material are you cutting?
Some plywoods can be particularly hard on bits. Some have very abrasive glues which will where grooves in the bits at the gluelines very quickly. Some will cause resins to build up on the bit's resulting in hotter running bits, which dull quickly.

To get the maximum tool life, you need to run at the highest chiploads you can. This keeps the bits cooler. Other than abrasiveness of material, heat is the main culprit in bits getting dull.
With harder plywoods like Baltic Birch, a chipbreaker compression spiral can allow higher feedrates, which in turn can give longer tool life.

Generally, if you're cutting 4x8 sheets, with maybe 6-10 parts per sheet, expect to cut between 20-100 sheets before the bits need sharpening. Cut quality will usually tell you when to change bits. If quality isn't that important, you can use a bit longer.

You can probably get a 3/4" bit sharpened 3-4 times. Sharpening will usually run around $20/bit, and each sharpening will remove around .015" from the diameter of the bit. So after 3-4 sharpenings, you'll basically have a 5/16" bit.

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Wow, thank you. That is some great information on bits. Very informative indeed. So after 4 sharpenings, you can do 4 more but as a 5/16" bit size?

Thank you,
Chris

Hey Gerry,

Just curious, what would you recommend as far as bits go for cutting acrylics and plexi? Really appreciate the info on the bits and how to make them go further, thank you heaps for your time to explain that to me. That was a golden bit of wisdom that I wouldn't have wanted to find out through trial and error.

What is your take on roughing bits for 3d relief work and contouring MDF? Also, are there better options to reduce post sanding on detail cuts?

Chris

Another option for plywood would be a single edge PCD compression tool. Like a compression spiral, it has up and down sections that will leave a clean edge on both sides. But being polycrystalline diamond, it will last eons longer than a regular carbide bit. Only drawbacks are that they cost 4-10 times what a carbide bit equivavlent costs, and they cannot be sharpened as many times as carbide.

Here's the link:
http://www.cnczone.com/forums/diy-cn...ptions-14.html

Wow, that sounds like an amazing bit though. 4-10times, hope they don't break!

Thanks for the thread link too btw.
Chris

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Originally Posted by Litemover

Wow, that sounds like an amazing bit though. 4-10times, hope they don't break!

Thanks for the thread link too btw.
Chris

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Depending on material, they can last 50-200 times the life of a carbide bit. Harder though usually means more brittle, and care should be taken with these bits. But I've been using them now on fire-rated G10 and other phenolics, as well as composite wood products, and they are awesome!

Use a single flute "O" flute for acrylics. They come in different geometries for hard or soft plastics, so choose the appropriate one.

If you're doing 3D routing in MDF, a carbide tipped 2 flute might be the most economical, but a little slower.
Do you want to reduce sanding on 3D MDF cutting? I do a finish cut .01 oversize, then coat with epoxy, let cure, and do a finish to actual size with about 5% stepover. Glass smooth with no sanding required. Time consuming, though.