Gallery, Projects and General > Project Logs
Mill Power feed
SPiN Racing:
OK Gang.. I see some awesomely good designs.
I LOVE my power feed on my mill. I was kinda indifferent when I got it, because I had no idea how useful it was.... Until I cut dovetails in the 34" long tool steel plate I am getting ready to divvy up for new tool holders for the lathe.
SOOOO
Here is the question.
Why not put a ratchet mechanism in the drive? Like the head of a 3/8" ratchet?? SO that while feeding.. If you are not close enough to the work after a pass.. you simply hand crank it closer. WHen you stop, if the ratchet mechanism is set properly, it will feed with power.
If you feed in the other direction, it simply ratchets, and has no load. So you could feed across a part.. then hand crank it in the other direction fast, and it would simply free ratchet.
I know of a type of drag racing transmission.. and I forget the name.. but IIRC it is similar to a helicopter transmission in that it only transmits power under load. Once the engine quits, or slows.. the transmission disengages and the vehicle or blades free wheel/spin.
Scott
John Rudd:
Hey guys...
Just read up on this...some good stuff..
One thing though I noticed..there's a theme running through this thread...
You are all running with a voltage regulator of sorts to power the motor for differing speeds....
Sorry but its the wrong way to do it...The lower the voltage the lower the torque from the motor...
Answer...use a pulse width modulated supply...
Arrghhh whats that you say?
Well its a bit of magic elecriccery that pulses the motor with the full supply voltage for a short period of time to make the motor go slow or applies the full supply voltage for a long period of time to make it go faster....
Want proof?
Easy....Take your motor and connect the wires across a car battery...hold them there for a minute or two...the motor runs fast yes? now flash one wire across one terminal or just dab it on and off...the motor now runs very briefly and soesnt run up to full speed but still has full power from the battery..... and max torque too...
I could cobble up summat if anyone wants.....
Darren:
I'm with you here John,
Although in practice lower voltages and torque don't seem to cause any problems, the motor still turns and the table still moves smoothly. The reality is that very little power is needed to move a mill bed. Even the bigger machines use small motors. Then you have to factor in the gearing ratios that keep the motor speed up whilst the output shaft speed is low.
However, I personally would like to see what you have in mind as the alternative.... :ddb:
John Rudd:
I would tend to use a 555 timer configured as an astable with variable mark/space ratio to give the pwm..Use a mosfet as the power driver device...something like an IRF 540...cobbled together the parts should be less than a fiver excluding tranformer etc...
Need the drawing? no probs..
I just bought a wiper motor from Ebay for £12...from a Ford Fiesta...that ought to do it..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=290325646440
Darren:
I have a question John....
If say you wanted half speed, you would set the timer to pulse the power delivered for 50% cycle time...
Wouldn't 50% on 50% off at full power be the same as 50% power continuous ?
eg, take 1HP for simplicity sake, 1/(100/50)= 1/2 power/torque
Also what about this pulsing power, I realise the freq would be high, but it would be pulsing all the same wouldn't it?
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