power feed?

[GalaticDan]

Hi,

I've been searching the web and theres not much on this topic. I'm researching power feed designs and ideas. I have some questions, does the feeder take the radial load when working with lathe tools? Or is there some kind of automatic opening and closing lathe chuck? (i.e. open, feed abit, then close) . Do the feeds go both ways, i.e. in and out during part maching to allow for longer part manufacture? Are there any reference designs? I've not found much on the web but have seen so many people building there own CNC machines, just wondered if someone else has tackled this topic?

Thanks

Dan

[acondit]

Dan,

Are you talking about something like a bar feeder? Or are you talking about a "power feed" for the carriage?

Alan

[GalaticDan]

Alan,

Sorry, I do mean bar feeder (NOT axis motor). Thanks,

Dan

[acondit]

Dan,

I am not an expert on this, but my understanding is that an automatic bar feeder would use either a power chuck or a power collet closer to open and close allowing new stock to be inserted to touch some stop for registration.

The videos I have seen show stock being inserted, machining done, then parted off and the cycle repeated.

I really don't know about this, but I don't see any reason why a machine couldn't be fitted with more than one stop and the bar "stepped in" for processing. I too will await more knowledgeable answers.

Alan

[BobWarfield]

There are a number of alternatives to a full blown bar feeder you might want to consider. If you've got a spindle liner and collet closer so you can manually insert a bar, you can have the machine advance that bar in a couple of ways.

First, you can do so semi-manually. Just have the machine position the tool as a "stop", and manually shove the bar forward until it contacts the stop before locking the collet again.

Second, there is a gizmo that includes a parting off tool as well as a clamp sort of thing. It parts off your finished part and clamps what's left sticking out of the collet. You release the collet and let the CNC program drag the bar out the desired distance. Relock the collet and have the CNC program release the clamp and go on about it's business.

Lastly, there is a coolant powered gizmo that also acts as a clamp. You can use it either in a powered tailstock or again as a tool. Position it over your workpiece end, turn on coolant flow to it, and it clamps down so you can use it to pull your bar on through.

I've seen all these approaches work, usually on gang lathes. I don't have the contact info handy on the two clamp-type gizmos, but they wouldn't be hard to Google for. I seem to recall the one integrated with the cutoff tool was called the "alligator". Maybe someone else has seen these.

Best,

BW

[Geof]

It is a case of all of the above; bar feeders come in many flavors. On small manual machines they were nearly always used in conjuction with a lever operated collet chuck. The driving force for the bar was often just a heavy weight pulling a cable attached to a push rod with a sort inverted live center on the end pushing on the end of the bar; the push rod being long enough to enter the spindle bore and push the bar all the way forward. Open the collets and the bar is pushed forward against a stop. The push rod was guided on a rudimentary track extending out from the machine.

Bigger machines had electrically operated chucks and feeders some large enough to take a bar twelve feet long and feet with the spindle running.

Compressed air bar feeders are also used where the bar forms the piston and is just pushed forward by the air pressure.

As BW mentions with CNC bar pullers are used which grip the bar and pull it out a programmed amount. These are inefficient because the spindle has to stop for this operation. Bar pullers can also be made to fit into the slot cut by a parting tool; partially part-off, change to puller, pull out bar and then finish parting leaving the next length ready for machining.

Haas, and probably other manufacturers, make a magazine barfeeder that can be loaded with many short lengths of bar which are fed under program control by a servo feeder.

We have two SL10s with shop made hydraulic barfeeders that use pressurized coolant at up to 300 psi to feed bar stock as small as 1/4"; the stock itself forms the piston. These are very efficient because the feeding can take place with stopping the spindle.

With CNC it is possible to program the stop position that the bar is fed up to so multiple advances are possible and it is possible to push the bar back into the chuck.

[acondit]

Dan,

I just saw a thread in the yahoo DIY-CNC group discussing bar feeders, if you haven't got enough info.

Alan