CNC turning on a gantry machine

[mike hide]

I was wondering if anyone has mounted a slow rotating spindle on the main machining bed so that one could essentially do on a gantry machine what otherwise would be done on a CNC lathe ?

I am thinking mainly in terms of a woodworking machine.

[cbass]

I think its called a 4th axis (or a rotary table). Look around on this site and you'll see many people doing it.

Carlo

[keyne]

search "indexer"

[joecnc2006]

Sample....

http://www.cnczone.com/gallery/showp...500/ppuser/223

[mike hide]

Thanks joe ...This is similar to what I had in mind except based on ignorance I thought that the forth fifth and sixth axes were angular move
ment of the spindle iin three planes .

What I had in mind was a similar set up only in the long axis ["X" axis] where the machine would first do the basic turning along the length of the workpiece as would be done normally on a lathe ,varying diameters molding shapes etc.

when that aspect was finished then the machine would come back and detail the turning along it's length. For instance lets say in the initial " turning" a half round form was made on the diameter ,then the machine in the second operation might come back and detail the half round to make it into an "egg and dart" molding

[Geof]

What is 'egg and dart'?

I have in mind doing what you are describing (I think). Setting up a rotary axis parallel to the X axis then carving the periphery of long cylinders; pillars when you stand them upright. This project is in its early stages and all I have so far is the gantry machine.

[mike hide]

I have included a couple of shots of "egg and dart" molding ....regards mjh

[Geof]

Yes that would look neat around the top collar of a 2' diameter 10' high pillar.

[ger21]

Originally Posted by mike hide What I had in mind was a similar set up only in the long axis ["X" axis] where the machine would first do the basic turning along the length of the workpiece as would be done normally on a lathe ,varying diameters molding shapes etc. when that aspect was finished then the machine would come back and detail the turning along it's length. For instance lets say in the initial " turning" a half round form was made on the diameter ,then the machine in the second operation might come back and detail the half round to make it into an "egg and dart" molding

No need to do this in two seperate steps. All can be done in one step, although you may need to do a roughing pass to get it clost to shape, then change tools to do the finishing pass(es). May depend on what CAM software you use, though.

[mike hide]

Yes I agree an initial "roughing out "operation would be required otherwise the depth of cuts could be too much, and could cause the operation to bog down .

Not being familiar with CNC operations If I may some basic slightly off subject Questions .

If you are "skimming" a flat surface and say the cutter [gantry] is traversing up and down the X axis, when the cutter gets to the end of it's travel does it jog over and cut the next tract in the opposite direction or does it disengage traverse to the start point jog over and start cutting the new tract in the same direction as the preceeding one .

Same situation except there is a web across the workpiece ,does progress in the x axis virtually stop while the cutter climbs over the web and then continue on the other side . seems to me there would have to be some anticipatory [if there is such a word] action on the part of the software to prevent the cutter balooning over the web.On the other hand is the software sufficiently sophisisticatedto recognize such a situation and perform the operation in the y axis instead or is that up to the operator to optimize the cutting path?

[mike hide]

I think this concept , as far as wood working goes is a viable solution to a sepatate CNC lathe . Just make a turning spindle superimposed on the gantry machine bed the 4th axis . This would make a separate lathe unnecessary at least as far as woodworking goes.

Digressing , spindle turning on a wood lathe is totally different to turning on an normal engine lathe . Thin material sections on a wood turning tend to part company at the most inopartune times due to the nature of the material spindleturning involves a slicing action . Turning wood on a metal lathe and using normal metalworking techniqies simple does not work very well.

However what we are talking about is using the spindle with endmills or router bits,in my opinion that should work.

Tell me why not you are not going to hurt my feelings

[Geof]

Are you meaning you would have this spindle just driven continuously but with the cutting action performed by a router bit rather than a chisel as would be done on a wood turning lathe? If that sentence is understandable.

I mentioned above that I am working toward something like this and it is not an entirely original idea. Quite a long while ago I met guy who had a very successful business making large wood columns for expensive houses. He had a big modified metal lathe; big as in 20 feet long with a swing of 30 inches. To turn the outside of his columns he mounted them between the chuck and tailstock and had a large router on the toolpost. The spindle drive was modified so it could turn very slowly and similarly the feed drive was also modified so it would feed at up to 1-1/2 inches per revolution of the spindle. He had a way of attaching a template along the back of the machine and had a system for disconnecting the screw on the cross slide so he could have the slide follow the template and turn tapers or barrel shapes. He also had an indexing system so he could lock the spindle and just move the carriage and with different cutters in the router could cut flutes the length of the column and these could also follow a template.

It sounds a bit like you are considering doing something that is along these lines but starting with a gantry router instead of a lathe. With full CNC of course you would be able to do much more detail.