[JFettig]

Hey guys, Im setting up belt drive on my mill, I got everything hooked up, I have a 1:1 ratio on pullies so 6000rpm on spindle. When I turn it on too fast it kills, I can slowly bring it up to speed and then grab the spindle and overload it and it stops.

The bearings spin pretty nicely now, its just really strange it does this. I have heard of others do the same thing but higher spindle speeds and never seen problems like this.

Anyone have any input for me? Im really anxious to start cutting stuff.

btw, The bear drive is totally gone.

[Ken_Shea]

Hi JFettig,
Assuming everything is spinning freely you with out a doubt have a motor with low amperage which ='s no torque. You can get a higher amp motor or change the gear ratio to decrease pulley rpm thus increasing power (torque) try 2:1.

You might also check voltage at the motor to be sure it is up to what it requires for full power.

Ken

[JFettig]

The motor is a 4.5A motor and it would be nice to get a higher amperage motor, I have a friend with some 2hp 24v motors that I may see if I can get ahold of one. I would love to just change the pully but I made them out of the only materials I have, I think Ill give some timing belt pullies a shot.


Jon

[HuFlungDung]

Jon,

What kind of motor are you talking about here? This is the spindle drive? What voltage is it running on? Single phase AC, 3 phase AC, or is it a DC servo, or what?

[Ken_Shea]

Jon, what information you have given is a little light for any recomendations. Let us know what this is on, voltages, AC/DC etc that should help myself or others to better understand what may be needed.

Ken

[Ken_Shea]

You're fast Hu, but in all fairness I did have 36 words to your 34

[JFettig]

I figured you would have assumed its the stock motor on the mini mill, its a 100vdc 4.5a motor. its pwm controlled and was gear driven with speed options 0-1000 and 0-2500rpm. It seems to not have the torque to run 6000rpm. I can spin it up to full speed and grab the spindle without any pain and overload it(same for any speed)

Thank you
Jon

[Ken_Shea]

Jon I learned many years ago to try and not assume anything.

There is no way (I can see) that a 4.5 amp motor turning 6000 is going to have any power. If another higher rated motor is not in the picture then gear reduction should be the logical next step.


Have you checked the voltage at the motor?

After thought:
The fact that it is the original motor on the mini mill one could presume it is of sufficient power, so low voltage may be the culprit.

[JFettig]

I measured 111vdc off of the motor, I saw it at 5.5a but ran round 4-4.5a.


I thought it would have had the torque, mainly because the guy who first told me about it said he had his running at like 7500rpm on the origional motor.

Does anyone have any ideas for pullies other than Vbelt? I looked around for timing pullies and I really cant find easily usable sized ones. How small can a 3/8 vbelt go without being too small? 1.125"?


Jon

[Ken_Shea]

Jon in one of your post you mentioned "0-1000 and 0-2500rpm" speed options, this is a long way off from 6000rpm, perhaps you are wanting more then the Mini Mill is designed for, and if you are, do you really need the extra RPM. Modifications can be fun and rewarding but not always practical.

On the 3/8" belt, if you are referring to 1.250 diameter pulley at the root, that should be about the limit. You could go to 1/4" belt.

[JFettig]

I was thinking that on the outside, thats why I asked. do I really need the extra rpm? probably not, but do I want it?

I guess Ill shoot for 3k rather than the origional 9k I was shooting for. Maybe someday when I get a bigger motor on it Ill shoot for 9k, or maybe when I get a bigger mill.


Jon

[Ken_Shea]

There you go Jon, that is being more realistic. Probably a lot older then you I can say that being dissatisfied with what you have will guarantee you will be dissatisfied with what you get.


Let us know how it turns out.

[JFettig]

How much torque does it take to run end mills 1/4" and smaller, down to 3/64"? I sure hope I can use those because Im going to give this machine a try tomorow! Ill be running them at 6krpm(carbide) will be machining aluminum and copper hopefully.


Jon

[Ken_Shea]

Jon what you ask is reasonable but too broad a statement to answer in a single post. Copper can be a bear to machine, soft aluminum is not nice as "WMS" once said "You can't mill bubble gum", aluminum alloy like 6061 is actually fun. Carbide is definitely the way to go. Knowing you are under powered I would suggest you keep the depth of cut low, may be .010 and the IPM at 5 for starters and increase it from there. If you have any amount to cut use coolant or some sort of lube and keep the chips out of the cutters.
Use a test piece if necessary before cutting the actual finished part.

Good luck and keep it fun!
Ken

[JFettig]

Thanx, I do plan on keeping the cuts to a minimum and the feeds to a minimum. Im guessing itll take hours to do the cuts, but I can handle it I think, I have been waiting months to cut something on this


Jon

[JFettig]

Well, I cut some stuff today and successfully, my new bearings are breaking in and its working a tad better.

http://jfettig.wc101.com/keychain.jpg

Jon

[Ken_Shea]

Looks real nice Jon, I must say your first cuts are much better then mine were.

Ken

[JFettig]

Thanx I took a pic:
http://jfettig.wc101.com/cnc.jpg

I gotta get er cleaned up a little

Jon