Woodworking

Bandwagon said:

I got one I knew was too small because I assumed there was going to be a multi-year learning curve and I'd recoup my money on the small purchase before funding a big one. A big part of that is because I have a full time job I love and a kiddo that takes up most of the rest of my time. I don't want to spend a ton of money on something I dont have much time for now.

If you're totally sure you're going to use it and want to hop in with both feet? Yea, get a 4x8 right out the gate.

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I'm not sure, but I am stupid.

Bandwagon said:

Rich and stupid? Get it, pussy!

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If I were rich I would have a servant post here. More like not poor.

Pretty good deal on Bessy parallel clamps. I bought two sets for an upcoming project. If you get more than one, split it into two orders so you can apply the $25 off coupon twice.

Does anyone have any recommendations for 3018 or 3020 size CnC machine? There's so many variations on parts and cheap Chinese fly by night companies in that segment.

Bandwagon said:

I don't suppose anyone has tips to fix chatter on a CNC with a long 4.5in endmill?

I'm trying to cut out the 2.7in thick walnut slab. I broke a bit a couple weeks ago when I got about 1.5in down. It bound up, I assume from heat.

I've got the replacement running today. I created a 2nd toolpath a little outside the other, to hog out some material and give a little more wiggle room. That's going fine, but getting a lot of chatter with this long ass bit. I have the machine paused right now.

YouTube research says that amateurs will increase rpm and slow down the speed, which is exactly what I did. Apparently I'm supposed to slow down the rpm and/or speed up the machine.

That sounds right? I don't want to wait another week for a new bit if I break this one


whoo Hekotat Cleetus-Meetbeetus K k^M

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4.5 inches!!?? Are you using a massive spindle? Please respond preferably with pictures. I'll be at a keyboard in about 20 mins to give a breakdown. You are playing a very dangerous game with a bit that large.

That's just a super long bit for the setup you have, plus it's thin. I'm kinda surprised it works at all and isn't just a shrapnel machine. Doesn't look like the right (or safe) tool for the job.

What cut are you making there? Are you eventually going through the material? If so, just use a saw. If not and you absolutely need a massive channel like that, consider a drill press with a fence (cleanup with chisel) or even a slot mortiser.

Bandwagon said:

I'll take pics in a sec. It's a 0.25in spiral up cut, and not a particularly powerful spindle. I'm not doing deep cuts....0.1in per pass. Material is on both sides, but I'm doing 2x toolpath now to clear some of the material that's touching. Give me a few mins and I'll take some pics

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I'm going to give basic information here that will be broad, please do not take any of this information as an insult to your intelligence. I don't know what you know and I just want you and others to be safe, I'd hate to see anyone here get hurt or killed.

Chatter can be caused by a multitude of issues and these things should be considered first before moving forward with such a large bit/job. Running long bits is dangerous and shouldn't be used unless your machine/collet/spindle are designed to run such things. I believe I have mentioned it here before but I can't remember so I'll just tell it again. We had a guy running a test on the production floor with a large bit that was not designed for the machine/spindle type and caused it to come out of the chuck at a very high RPM, it shot across the floor bouncing all over the place and impaled in his leg barely missing his main artery. We were forbidden to run anything over 2.5" in length unless the machine was surrounded by a bulletproof glass barrier. Be very careful here, just because you have done it before doesn't mean something similar won't happen to you, it just takes once to hurt, maim or kill. Also keep in mind that drywall will not stop something moving so fast, so keep your loved ones safe if you're doing this in your garage. It's some scary shit when you see a bit bouncing around at 18k-20k rpms and having no idea where it's going to go next.

Chatter Main issues

• Collet depth
  • If you do not have enough of the tool inside the collet this will cause wobble/chatter. This can cause the collet to become worn out and eject the bit. This will also cause your spindle bearings to wear out.
• Carriage harmonics
  • This is the best way I know how to explain this, if the carriage is not built to withstand the type of pressure being applied at those lengths this will cause the entire carriage to chatter and tear itself apart. Only our largest machines were capable of using such large bits.
• Spindle size
  • This ties in with the two items above, larger spindles are designed for larger bits. They can withstand the horizontal pressure applied with such lengths. Think of a cheater bar used to bust a nut loose, you're applying a ton more pressure to the bearings/collet/carriage/etc. When using a bit of this length.
• Bit quality
  • Ensure you are using a good quality bit, if a bit at that length is not balanced properly there is nothing you can do to stop the chatter.
• Bite size
  • Ensure the cut depth and bite size being cut out per pass are very shallow. This will help reduce chatter.
• Flutes/chip load/etc.
  • Number of flutes, upcut/downcut, RPM, Cut speed, etc. will all play an important role in reducing chatter.
  • Going too slowly with a cut-speed will cause the bit to bounce off the wood, it will also cause the bit to overheat which can increase the size of the bit and cause it to make more contact with the wood causing even more chatter. This will also burn up/dull the bit very quickly which will compound the issue further.
  • If your bit is a downcut this will also put more pressure/load on the bit which will cause more chatter.

I'm not saying you can't do this, you can. You just need to be careful, very careful. Mechanics will play a huge roll in the chatter, Check all your bolts make sure they are tight, ensure your collet is not worn out, ensure your spindle and collet are designed for such a lengthy bit. if all this looks good you need to experiment with your RPM/Bit Site/Cut Speed until you can reduce chatter, more than likely with a smaller machine and a bit that long you are going to be cutting very slowly. Upcut/Downcut bits can have dramatic effects upon the wobble as well. If you are having to go so slow that it's burning the wood then you may need to re-think your process. If the bit is too long there is simply nothing you can do to prevent chatter and it will have to be cleaned up post process.

The best thing about CNC machines is there is always a undiscovered solution to your problem or a common one. If you plan on cutting things this deep in the future you can always get two pieces that are half as thick and cut them in two jobs then use a dowel pin or whatever to join them back together. You could also try to use a shorter bit to go down as deep as you can to reduce the amount of material you are cutting out then finish out with the longer bit.

As for feed and speed tinkering, I'm not as well versed as others in this field. I typically looked at the Onsrud manual, changed my settings and went on my way unless it sounded funny. Then I'd adjust on the fly until it sounded right, which were typically minor adjustments.

Please be careful.