Spindle and drilling?

[dttworld]

Why do some people say you should not use a spindle for drilling? What are people using instead?

thx

[Brady Watson]

For production cutting, some use an air-drill, while others use something like a Milwaukee drill. It boils down to what material you are drilling more than anything else. There are a few things to keep in mind when drilling with your spindle:

First, you should never drill metals with it. The spindles equipped by ShopBot are not 'drill' rated - the bearings are radial and not Timken roller style bearings setup for thrust loads...so you have to keep that in mind or you could skid & gall your ball bearings & races.

Second, for most jobs in wood and other relatively soft material, drilling is usually fine, although I recommend using the peck drilling option under the drilling toolpath strategy. It will go down your stepdown depth, retract to clear out chips & then go down the next increment (stepdown distance) until it gets all the way through.

Third, your bit selection is important. You must make sure that you use a center-cutting bit when you drill. If you got the SB Starter Bit kit when you got your tool, the 2-flute 1/2" straight, 1-flute 1/4" straight and 1-flute spiral-O bits are not center-cutting. That is to say that there is no cutting flute along the center of the tool to clear away chips when they are plunged straight down. If you look at the 1/4" upcut and downcut spirals, you will see that they are 'sorta' center cutting because they have a fish-tail tip on them. All of those bits except for the V-bit & 1/8" ball end mill are considered non-center-cutting, and all but the 1/8 ball are router bits. They are designed to cut sideways...not really plunge straight down. So during normal cutting, you would ideally want to choose a ramped stepdown. End mills for the most part, are center-cutting, and aside from the absence of the fish tail end, are identical in grind to an upcut spiral router bit...end mills are great for all kinds of general cutting, including drilling. If you do wind up using a non-center-cutting tool, you will put a substantial load on your bearings and really load the Z motor rack & pinion because you are essentially compressing the material in the center of the bit that is not being cut. I've lifted the entire gantry off of the rails on my PRT in the early days before I understood about non-center-cutting tools :D

Finally, if you do have a need to drill metals (non-ferrous), you'll have to go about it in a round about way, knowing how AL loads up cutters when you plunge straight down, and that the spiral-O tools are not meant to be plunged. Just draw a circle and then choose an inside profile toolpath strategy. Choose a tool that is at least slightly smaller than the hole to drill and choose a spiral stepdown ramp/plunge. This is the most efficient way to drill metals, and also the safest for your spindle bearings.

-B

[Ajcoholic]

I am sort of confused when it comes to this drilling stuff, and the spindles.

Is it safe to drill wood, with a twist drill bit? Or is that an absolute no-no? I am thinking from what you are saying, no.

AJC

[garyc]

Andrew...
For wood the best bits are carbide tipped boring bits (like line bore machines use) with the rpm at or under 5K rpm. Torque on the spindle is down at that rpm, so adjust plunge speeds accordingly.

Most twist bits are designed to run at 3500 rpm and lower. Personally I wouldnt trust one in a spindle.

[dttworld]

......

Third, your bit selection is important. You must make sure that you use a center-cutting bit when you drill. If you got the SB Starter Bit kit when you got your tool, the 2-flute 1/2" straight, 1-flute 1/4" straight and 1-flute spiral-O bits are not center-cutting. That is to say that there is no cutting flute along the center of the tool to clear away chips when they are plunged straight down. If you look at the 1/4" upcut and downcut spirals, you will see that they are 'sorta' center cutting because they have a fish-tail tip on them. All of those bits except for the V-bit & 1/8" ball end mill are considered non-center-cutting, and all but the 1/8 ball are router bits.........
-B

Thanks for the bit descriptions that came with the starter pack. Now I know what to Google. Surely there has to be an FAQ some where for CNC router newbies (you should make one based on your posts). I guess I need to think of the spindle as similar to my Dewalt router versus the low RPM R8 spindle on my mill.

I'll probably go through the effort of rigging up an AC corded drill since an air drill might annoy my neighbors.

[Ajcoholic]

Andrew...
For wood the best bits are carbide tipped boring bits (like line bore machines use) with the rpm at or under 5K rpm. Torque on the spindle is down at that rpm, so adjust plunge speeds accordingly.

Most twist bits are designed to run at 3500 rpm and lower. Personally I wouldnt trust one in a spindle.

Got it, and thanks! You guys are great for info, thats for sure!

AJC