Breaking way too many bits

Whats wrong with my settings? Any ideas? Am I going too fast, too deep? How do you guys handle it? Are there better bits that don’t break? I am trying to cut birch plywood with 1/16 inch bits and they are breaking all the time…

Can anything be done?

Can you give us some more details about your bits? (2 flutes, spiral, …)

Also, how far out of the collet do they stick out?

Also, when you tighten the bit in the collet and manually turn the spindle on, do you see any visible runout? (does the bit seem to get wider than it is)

There are all kinds of reasons that bits get broken, so the more details you can provide us about your machine the better. Have you double and triple checked that your machine is dead on square in all directions? Is everything tightened to the right amount and not over tightened? etc. etc. etc.

I have not broken a single bit yet. Chances are your feeds and speeds are not matched. There are chip load calculators that will give you your feed rates. I have managed to do very well with an 1/8" upcut on hard maple at 100 in/min and could probably go faster but would lose cut quality.

1 Like

Hey Nick,

I haven’t broken any 1/8inch bit yet either, those seem very robust. However the 1/16 and 1/32 inch bits are breaking all over the place… I am using a quarter of the bit diameter depth per pass and a speed of 600mm/min…
I think thats about almost as shallow and slow as it should get for plywood…Its not like Im milling aluminium.

Hey sketch,

These are the ones I am using… Broke 6 in 2 days…
They stick a bit more than the area where they start to get narrower. The bit gets great concentricity and no runout. My machine is super built and checked and everything(Engineering MSc), but it just keeps failing at some basic materials…

There is a screw on my X carriage that falls off always after about 30 mins of milling. No matter that what I do, it will come loose and fall off…

1 Like

Any chance you have any other 1/16in bits around? Maybe the one from the Inventables starter kit?

I just cut some MDF with a 1/16in 2 flute spiral up-cut at 950mm/min and .9mm depth per pass. I have a set of 10 from Inventables and it will take me a good while to go through that set.

Your feeds and speeds look like they should be fine, but when I saw the price at less than $8 for ten, I begin to wonder at the quality of the bits in question.

Another question is what is the RPM you are running them at? That would be another key to the Feed/Speed equation.

For that screw, try a bit of Loctite.

The 1/16 bit I got in the starter kit from inventables broke on a piece of mdf on the first day with 0.6mm depth and 650 mm/min…

I entered 15000 as my RPM, not even sure if the 24V DC spindle can go that fast, but thats what I have in my settings…
What kind of bit would you recommend for some detailed work in plywood? I am cutting brooches for my wifes business and at this point Ive broken more bits than I have cut out brooches…

I’d use 1/16in or smaller for small detailed work. When working on Jewelry I use 1/16in or 1/32in bits. I have broken 1 of each, but it was because of running them into a clamp or something. One other bit I might use for super detail stuff is a 20 degree engraving bit, but only for tiny fine lines.

14000 is the top end of the 24v Spindle, so anything over that will just default to 14000.

Really the feeds and speeds look fine to me. Maybe others can chime in here with a yay or nay on them.

My mind keeps going to squareness and if the travel of your bit is coplanar with your work surface… One thing that I always do when working on small detailed pieces is to make a pocket out of something like HDPE that I can put my working material into. That way I am always sure that the base is super flat. I usually use a larger 1/4in 2 flute straight bit for this, but I have to make sure that it is super straight in the colette. To do this, I tighten it and turn on the spindle and listen for louder than usual noise and look for any runout. If I hear any or see any, then I loosen and go again until it is right. (also sometimes the bit needs a little push to one side or the other, but the spindle should be relatively quiet when just spinning at 14000 in the air)

Once I have the pocket made, then cutting with smaller bits into the material becomes a lot easier. The surface of the wasteboard can have mounds and bowls in it with differences of 1mm or even 2mm and pocketing a fixture in this way, helps to eliminate that.

Try this: on a piece of scrap, mill out a pocket about 3 or 4 inches square with a 1/8in or 1/4in flat end mill. Take a l at the bottom of the pocket. Is is really flat? Would it require a lot of sanding to get it flat? Does it have big ridges about half the width apart as the width of the bit? Answers to these questions might help diagnose the issue.