Slant-Bed CNC Lathe Build

[barnbwt]

I had a dumb idea for the 1" 'live tool' sockets; rather than the simple solution of a pair of set screws on the underside, have a concave-wedge between each pair of tools pulled upward by a bolt through the tool plate. The added complexity seems to carry a number of advantages; I can see this scheme having more surface area/rigidity than set screws, it puts the fastener heads on the top side of the tool plate, and 4 fasteners would hold five tools.

Next dumb idea; form the obnoxiously-deep bores in the tool plate with sleeves inside an epoxy-sand casting. As large (8x12x3.5) as the block has become, a casting makes much more sense than machining. The density of holes may still be too great for that, however; I have no idea how brittle that material is. And of course the various component & tool mounting surfaces would also need to be metallic inserts set into the casting.

I also had a less-dumb fabrication question; whether anyone has tried one of these 'weldment frame' builds using brazing; braze is plenty strong, causes less warping/stress, can be applied in an oven (though with a ton of prep-work), and would seem to have damping benefits over welding.

 

[JimDawson]

I like the wedge idea. The only downside might be that if you wanted to change one tool, you might disturb the setup of the adjacent tool.

I assume the bores would be through the 8 inch dimension. The bores would not have to be on-size for the full depth, just deep enough to accommodate the tool holders plus some clearance. A reamer would work well here. The balance of the bore could be an oversize counterbore from the back or a drilled hole that is smaller, or maybe a through hole would not need to be drilled at all. The difficulty of making the part depends on what equipment you have to work with when building the machine, this is something that could be done on a BP type knee mill. I would just build the block out of a chunk of 4150 or 4340. It might take a couple of days to build it, but you only have to do it once.

 

[barnbwt]

I like the wedge idea. The only downside might be that if you wanted to change one tool, you might disturb the setup of the adjacent tool.

I assume the bores would be through the 8 inch dimension. The bores would not have to be on-size for the full depth, just deep enough to accommodate the tool holders plus some clearance. A reamer would work well here. The balance of the bore could be an oversize counterbore from the back or a drilled hole that is smaller, or maybe a through hole would not need to be drilled at all. The difficulty of making the part depends on what equipment you have to work with when building the machine, this is something that could be done on a BP type knee mill. I would just build the block out of a chunk of 4150 or 4340. It might take a couple of days to build it, but you only have to do it once.

Maybe do the 'wedges' as plugs tangent to the 1" holes? That would have one screw for each tool. Rather than a wedge, I'd take a 3/8" or so rod, mill a 1" diameter 'mouse hole' in the side that engages the tool, and blind drill/tap the end the tension screw goes into. I think I've seen Chinese boring bar holders done that way, usually with the plugs in pairs. That would take up about as much room as a simple bolt, but provide more contact surface & mechanical advantage (that you can also access from the top side). I think smaller-diameter tools could still be used if a split-ring clamp or sleeve was employed.

To be honest, I'd actually planned on boring all the longitudinal holes with the machine itself, flipping the plate around 180 degrees if needed (obviously the holes from the first setup would be the 'not-precise' holes). The only reason for the through-hole is so cables or hoses could pass through. I also had the crazy idea that a die-holder could be fastened across the front of a 1" hole and the stock run through it (simply because the stock is at most 1" for longer parts). Right now the tool plate is 12" long, so the motor & ball screw fit neatly between the X guide rails, which for ~1" drills seems like it's getting a bit long. For the MT1 tapers, the ~3/8" through-hole for the drawbar would require an aircraft drill or cable drill.

I found (maybe) an affordable jig-borer which would be perfect for truing up the holes as well as the spindle taper;
1) predrill 3/4" x 2" holes in the tool plate using the unground spindle w/ runout (spin the block & repeat if needed, with first holes oversized)
2) set the jig borer into a hole, lock it in place
3) turn the spindle against the grinding stone along the desired taper & diameter to true it up
4) drill out the tool plate holes to near full size (and drill/ream out the MT1 through & taper holes)
5) set jig borer into the spindle, adjust it to grind out the holes to full, concentric diameter (maybe the MT1 tapers, too, if the stone can reach)

All that would be needed to be done before hand is;
-The slots for the square tool holders & clamps
-The threaded holes for the underside mounted parts
-The stepped through-holes for the wedge-plugs holding the 1" tools
-Maybe a grid of smaller tie-down & alignment pin holes on the top surface, in case I ever mount anything up there for milling?
-Maybe some mounting points on the upper/lower (along X) faces, for indicators or cutting oil nozzles or something?

That seems way more reasonable than effectively machining an engine block beforehand

 

[JimDawson]

Sounds like you have it under control. I like the idea of doing the work in the machine.

Two locking mechanisms come to mind, first is a D1 chuck cam-lock system, and second, take a look at the Dayton Lamina Ball-Lock system. https://www.daytonlamina.com/sites/default/files/doc/920_BallLock.pdf Both would be quick change, but maybe more trouble than they are worth.

All of my round tool holders are secured with set screws. The normal lathe tooling is secured with a wedge lock system designed for square shank insert holders that bolt on to the turret. Each of the turret stations is ported for through coolant, very handy for drilling, boring, and tapping operations. Puts the coolant right where you want it. The through coolant is only ported to the active tool and is fed from a pump separate from the flood coolant system. I can post some pictures later if you want.

 

[barnbwt]

Sure, I'd appreciate that. Like I said, the primary draw to alternative fab methods is due to the size of the toolplate; gonna be hard/expensive to source and process material at this size.

 

[JimDawson]

Here are some pictures

Square tool holder. No, the picture isn't upside down, that is the way the tool presents to the work. Note the wedge system.


One of the round holders, this one is 1 inch. Ported for coolant. If you plug off the front port, you can run coolant through the holder. Sitting on one of the square tool holders without the wedges in it.


A 1 inch round holder with an ER32 collet chuck in it. The ER32 is ported for through coolant, the aluminum plate on the back of the tool holder is the rear block off plate for coolant. The coolant squirts out of the slots in the collet at an angle, pretty well aimed right at the drill tip.


This port is where the coolant is fed to the turret, there are a series of passages inside the turret to pass the coolant. Only the station that is in working position gets coolant. The tap is in the working position. The device to the left is a bar puller, a must have if you don't have a bar feeder.



A tap in a ER11 holder, 3/4 shank, also has through coolant.


Here is a 3/4 drill bit directly in a 3/4 holder. Note the slot ground in the bit, this is where the coolant comes through, one on the top, one on the bottom. A block off plug is installed in the coolant port.


And the flood coolant system. The aluminum welding rod C clamped to the tool setter arm is a visual guide to position parts that we were inserting by hand.


You can just see the turret coolant feed tube at the very top, right of the carriage, just below the end the light



Maybe you can get some ideas from this. The thing at the bottom right of the picture above is not a tailstock, it's a part catcher without the basket on it. At the extreme lower right is the part conveyor, you can just see the edge of it. This lathe is not equipped with a tailstock.