[TTalma]

I am working on a project where I need to drill lots of holes in 1/4" MDF. After lots of testing I got some bits that have good tool life and figured out plunge rates that keep it pretty cool. The bit lasts about 600 holes, and is hot to the touch after 25 holes, to hot to touch after 50.

But I found that if I run the spindle at 5000rpm the bit stays cool enough that it never really gets hot. I tried drilling 50 hole like this and the bit was still cool to the touch.

My spindle is marked as the operating speed to be 12,000 to 18,000 rpm. What will happen if I run it slower at 5000 rpm for drilling the holes (there seems to be no performance issues), I have to drill about 8300 holes by the time I'm done. Takes about 2hrs to drill 600 while getting good results. Then 15 min to cut the parts out.

These are vent and screw holes for a case for little gaming consoles based on rasberry pi's for middle school kids (gamepi). My youngest volunteered my CNC to cut the parts for 142 cases for their tech class (58 holes per case). Awesome project and these kids are learning a ton since they are excited for the end result.

[Al_The_Man]

If a high speed spindle is ran lower than the rated speed it will overheat, or likely to. With burn out possible.
The hi-speed variety are constructed with less iron in the stator, therefore do not posses the inductive reactance required at lower speeds in order for the current to be sufficiently low.
All you have is the actual resistance of the winding, which is extremely low.

[joeavaerage]

Hi,
is your spindle air cooled? Many are, they have an impellor mounted directly on the shaft. Impellors work at roughly the square of the speed, thus running it at
half speed will result in approx 1/4 the airflow....not good. It gets worse at lower speeds.

To combat the poor air cooling at slower speed many people use a separate electric fan to blow cool air through the motor. It might help.
I have seen people use a small pancake fan....and the motor cooked up! If you are going to do it use a decent fan, otherwise you will cook your
spindle for sure.

Craig

[Al_The_Man]

Is it worth taking the chance?
Too late once its fried!

[joeavaerage]

Hi Al,

Is it worth taking the chance?

Quite so, I never run my spindle below 12000 rpm, and only lightly even then. I'd cry genuine tears if I fried my Mechatron spindle, I haven't done
so yet...after eight years.

Craig

[TTalma]

Is it worth taking the chance?
Too late once its fried!

No its a Columbo atc. I can burn several hundred bits cheaper than replacing the spindle.

It uses an externally powered fan for cooling. It's mounted to a large aluminum plate as well. I've never had heat issues. But I rarely do long runs either.

It's never been hot enough that you couldn't hold your hand against it. No reason to start now.

[mactec54]

No its a Columbo atc. I can burn several hundred bits cheaper than replacing the spindle.

It uses an externally powered fan for cooling. It's mounted to a large aluminum plate as well. I've never had heat issues. But I rarely do long runs either.

It's never been hot enough that you couldn't hold your hand against it. No reason to start now.

Seeing your spindle has the built in fan, if you contact Columbo you may be surprised with your spindle as some of there spindles with the built in cooling fan can go very low in the RPM's, what will make it heat up is as you go lower with the spindle speed, the amp draw may go up, and this causes the over heating in your case, so not always the lack of cooling on a spindles like what you have, the spindles with a fixed fan mounted on the end of the rotor are the problem spindles when going slow

what is the Kw or Hp of your spindle, 12,000 RPM is where it has it's max torque, so if you have 5Hp then at 6,000 RPM you will have 2.5Hp, the RS Series spindles can run from 0 to 24,000RPM, even though you see 12,000, to 18,000 on the name plate. at the low speeds the torque will drop and the heat will go up, what size drill are you using.

The best running Temperature is 115F to 130F, so if you have an IR Temperature gun, then you can keep it in this range and you will have no problems, they are tested at over these Temperatures I have listed, these are a safe running Temperature

[kinghong1970]

Sorry for noob post but…

1 flute up cut with pecking motion a viable option?

To reduce time endmill spends rubbing against the MDF?

Or increase plunge speed?

If tearout is issue with up cut, do light cut with down cut endmill first then go with up cut?

[dazp1976]

I wouldn't risk it myself.
I'd look at bolting on an add-on like a used mini mill motor/controller or something along those lines.

Although.
Pecking the holes at 12k with carbide or co8 bits is prob the way to go with this.

[TTalma]

Seeing your spindle has the built in fan, if you contact Columbo you may be surprised with your spindle as some of there spindles with the built in cooling fan can go very low in the RPM's, what will make it heat up is as you go lower with the spindle speed, the amp draw may go up, and this causes the over heating in your case, so not always the lack of cooling on a spindles like what you have, the spindles with a fixed fan mounted on the end of the rotor are the problem spindles when going slow

what is the Kw or Hp of your spindle, 12,000 RPM is where it has it's max torque, so if you have 5Hp then at 6,000 RPM you will have 2.5Hp, the RS Series spindles can run from 0 to 24,000RPM, even though you see 12,000, to 18,000 on the name plate. at the low speeds the torque will drop and the heat will go up, what size drill are you using.

The best running Temperature is 115F to 130F, so if you have an IR Temperature gun, then you can keep it in this range and you will have no problems, they are tested at over these Temperatures I have listed, these are a safe running Temperature

I don't have a heat gun, but It ran for about 3 hours last night (with pauses for material changes) at 12000rpm. After all that time the spindle was only warm to the touch.

My spindle is a 6.6hp, and I'm drilling 2mm holes, so power is not an issue, based on your comment at 5000rpm I would have ~2hp available, plenty for these holes!

[TTalma]

Sorry for noob post but…

1 flute up cut with pecking motion a viable option?

To reduce time endmill spends rubbing against the MDF?

Or increase plunge speed?

If tearout is issue with up cut, do light cut with down cut endmill first then go with up cut?

I'm using normal 2mm twist bits, much cheaper than a router bit.

I tried pecking, but with only 1/4" material it didn't seem to make a difference.

[TTalma]

I wouldn't risk it myself.
I'd look at bolting on an add-on like a used mini mill motor/controller or something along those lines.

Although.
Pecking the holes at 12k with carbide or co8 bits is prob the way to go with this.

This is probably a one time thing, so not worth investing in a machine upgrade. Although I did find a drill head for my spindle, basically a speed reducer, but they are a few grand new!

I purchased 25 cheap Chinese bits on eBay for this job, and have about 17 left. I bought a few good bits, and only got slightly better tool life. The bits are blued and the holes were starting to burn when I switched bits, at 580 holes. So it's heat killing the bits.

When I was lying in bed last night, I had an idea that I will load 5 tool holders with these bits, I get 15 parts from one sheet. 3 rows by 5. After cutting 3 parts it's at the side by the tool rack, I will just have the machine swap tools (I.E. Tool holder 1 drills row one, tool holder 2 drills row 2 etc.) This should give the bits a chance to cool completely. Then I'll see if I get better tool life. And it should only add a min or 2 to the cycle.

In either case I am about 1/3 done with the job, and will definitely be done this weekend.

I think if I'm asked to do this again, I'll talk to the teacher about the design, and change the holes to slots, then it would only be 6 screw holes per part.

[mactec54]

I don't have a heat gun, but It ran for about 3 hours last night (with pauses for material changes) at 12000rpm. After all that time the spindle was only warm to the touch.

My spindle is a 6.6hp, and I'm drilling 2mm holes, so power is not an issue, based on your comment at 5000rpm I would have ~2hp available, plenty for these holes!

Then you can run at a much lower speed 2000 to 3000 RPM will be fine, the spindle temperature won't change much as it is not doing much work, with a 2mm drill

[TTalma]

I tried my idea of switching tools after every 3 parts, which is 174 holes. Seems to work pretty good, I made another 45 parts, so I'm about 2/3 done now. the drill bits all seem to be fine after this. I hope to get in the shop tonight and finish up.

But drill, move 4mm, drill, move 4mm, drill, move 4mm etc. etc. etc. Is boring! takes

43 min to run the entire thing 32 min is drilling holes.

[TTalma]

Ran quite a bit through last night and the bits still look/perform good. I only have 30 more parts left to do, so we'll see if they hold up. I'm expecting they will.