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Jonathan is quite correct about friction, a really important mod is a one shot oil system. This will reduce the wear and reduce the friction its the only way to get the lube in just where its needed, just a PITA to do.Quote:
Originally Posted by Jonathan
Phil
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I have a similar mill,i have 70v ps running at 6 amps rapids at 2000 mm pm motors are 4Nm I would say that to be the minimum spec.Quote:
Originally Posted by h4ppy-chris
Increasing the power via belts will also reduce the max speed unfortunately speed costs money.
Phil
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Well, having done the calcs on my mill, and measured the actual friction coefficient with a digital spring gauge, I know the likely motor is going to be in the order of 3Nm to achieve 1300mm/min cutting and 2500mm/min rapids. If I hadn't measured it then the estimated friction coeff of 1.1 would have suggested a 4Nm motor. I'm working on 36v @ 4A as I have a 36v, 12A PSU to hand.
The point here is that every mill is different. You need to weigh the table and measure the friction coefficients to avoid overegging the solution. I am not fussed about cutting speeds as long as they are reasonable... its still going to be faster/more accurate than I can do it by hand and since I dont have suds or one-shot oilers I'm going to have to be there to spray/oil as it runs.... Its not going to be working hard enough to justify doing those mods...yet...
Those numbers are similar to what I got on my milling machine with the same motor. I've never cut at over 1000mm/min, and that was with a big cutter (http://www.youtube.com/watch?v=iC7lX..._order&list=UL). The 2150rpm spindle limits the feedrates I can use. I started off with 2500 on the X axis (see http://www.mycncuk.com/forums/showth...ll=1#post12790 post #19), but have gradually reduced that to 1800 over time. Now I've taken the motors off to use them on the router. It will still do more than 1800, but not 2500...I think the ACME screw or something has worn a fair bit. Time for ballscrews perhaps-that should make it a bit faster due to the efficiency.Quote:
Originally Posted by irving2008
Attachment 3516
Looks like a Clarke MD25 - Similar to the Warco MD30/Minor i have.... tho mine has a longer table... I wont be using the original screws but some ballscrews I got off Robin..... the top speed of the spindle is limiting, I have a VFD to go on so plan to increase the belt ratio to up it to 3000 or so... tho running at 1800mm/sec with a 6mm cutter would ideally like 5000rpm on the spindle... not sure the bearings will like that much tho...
If that's mine your referring to then it's a Clarke CMD1225C from Chronos (though I got it second hand). The castings look pretty much the same. Agreed with the 5000rpm. I'm thinking either mount a separate spindle to the side of the main one (i.e. my 6000rpm 6kw-ish brushless motor), or put that same motor in place of the 750w original motor. I was about to ask you if you thought the bearings would take that rpm! They allready sound a bit rattly and the spindle pulley gets warm - maybe that's normal. How long is your table and what are the travels just out of interest? I get 350x141x92mm.Quote:
Originally Posted by irving2008
What diameter are your ballscrews?
The table on the MD30 is 675 x 205mm approx and the travels are 490 x 195 x 105mm approx. The ballscrews are 16mm dia. I'm pretty sure my quill bearings won't like 5000rpm, they get warm on 2150! I was considering a secondary spindle based on an ER collet chuck, belt driven 1:2 or 1:3 off the main one, similar to what Robin's done (but probably nowhere near as neat :lol:).
Can you not up the frequency instead ?Quote:
Originally Posted by irving2008
I renewed my bearings with SKF they are rated at 7K
I have run mine at 3.5K but I need to change the belts as I have the twist lok type and you can see the effect of centrifugal force. Scary
I do intend to go to 5K
Phil
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i have some worn A-belting... its starting to fray :lol: yes I can take the motor higher on the VFD but not from 2150 -> 5000 using the same pulley set. You can over rev the motor maybe 10 - 15% say 2500, but what I plan to do is put a new small fixed pulley on the motor and run a single belt (with an idler to get round the column) using the largest pulley on the spindle.
Irving I am gonna have to disagree.
My motor speed is 1400 and as you know they also come in speeds of 2800 so it depends on the stock speed
I have run it at 100Hz for long periods the motor does not get warm in the slightest.
Who told me I could do that, the company who sold the motor inverter package to me.
The motor upgrade was forced on me due to the fact that the original motor over heated and was poorly balanced.
So it turned out a blessing in disguise.
Phil
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