Achieving positional accuracy on subplate holes?

[Donkey Hotey]

I've got a gaggle of Chick vises that I want to make a subplate for. Chick vises are designed on a 50mm basic pin and bolt spacing. The vises have two precision locating holes on the bottom that are 12mm diameter and either 50mm or 100mm spacing (4" or 6" model respectively).

Chick sells subplates for exactly what I want to do. The only problem is that they're pretty spendy and they're generally larger than I want, so I'm designing my own.

I want to create a precision row of 12mm holes on 50mm spacing. I plan to use these with locating dowels for the vises. I would like the dowels to be located precisely enough that the vises will be square every time, using only the dowels. I'm not worried about the machine getting the holes right; I'm worried about how accurately the drill will track the spotted locations (wandering).

So the question: which will create the most precisely located holes?

• Start with an NC spotting drill, then cut the holes using a stubby drill at a moderate RPM and finish with a reamer?
• NC spotting drill, pilot drill, then use a 4-flute mill (more rigid than a drill) to cut the holes before reaming?
• Or should I ditch the whole 'drill' idea: create undersized holes, then finish them with a boring bar?

Thanks in advance,

[Geof]

Interpolate them.

Although to answer your question about the most precise method boring is the way to go, but interpolation is good enough I think.

[Donkey Hotey]

Thanks, Geof.

Since I'm going for absolute squareness of the pattern and I already have the boring bar, I think I'll go the boring route.

Any other subplate tips? Should I bother bushing the holes? Should I helicoil the 12mm threaded holes? Can I trust keying the subplate to the VF-2's table or should I plan on tramming the plate every time?

[Geof]

Absolute squareness of the pattern comes from your machines X, Y positioning accuracy and is not dependent on how you finish the holes.

For best precision bushing the holes is a good idea and for best thread life using inserts is a good idea. Not helicoil because if these get damaged they are pretty much non-removable. I have seen threaded inserts that have something like 9/16"NF on the OD and 3/8" - 16 in the ID with a slot to screw them in or out; these can be replaced.

Keying to the table is also handy but whether you also choose to tram the plate depends on the precision you need. Keys will probably not give you much better than +/-0.0005" so if you have a dowel at each end of a subplate 24 inches long it will go back to within half a thou per foot parallel to the table slots.

The problem with keys is that they do not give you longitudinal positioning because they slid in the table slot. If you want really good precision for replacing the subplate install steel bushings and then drill and ream these for tapered pins going into the surface of the machine table; this gives you very precise positioning in both X and Y. If you do this make sure the tapered pins have the top end tapped for an extractor screw otherwise you will have trouble removing the plate.

Incidentally 12mm is quite large for the threaded holes. I use 3/8" and sometimes find the clamps or bolts interfering with tool access; larger bolts would be worse.

[RICHARD ZASTROW]

Another thought on holes: jig bore reamers? Maybe it's just us old farts who use them anymore. lol

Dick Z

[Donkey Hotey]

Thanks again for the tips.

The 12mm bolts are chosen because that's what Chick uses. All the vises are predrilled for 12mm, counterbored, SHCS. Chick also uses 12mm dowel pins on all of their surfaces and other features (end plates, top plates, etc).

The subplate won't be used for anything other than holding the Chick vises, so fastener clearance won't be a consideration for other setups.

The dowel bore is right under the center jaw and passes all the way through. The center jaw uses this same bore to locate. So (in theory) if the vise is doweled properly and the center jaw is drilled square, the center of the hole in the center jaw is also the center of the dowel hole in the subplate.

As for the longitudinal placement of the subplate, I'm not worried about that; I'm only interested in squareness to the machine. I guess I need to tram the slots and see how square they actually are.

In use, I'm going to use the Renishaw probe to pick up the first dowel hole and use that as my XY origin. The rest of the vises will then be in a predictable pattern.

That's why I need to be able to trust the locations. The Chicks are going to have oddball geometry machined into each jaw. There will be no repeatable features to pick up for future work setups and I have to trust that they are in the right place when I drop them onto the pins.

Originally Posted by RICHARD ZASTROW Another thought on holes: jig bore reamers?

Thanks Dick, but I don't have a jig borer. I have to price this whole thing out so I don't spend more than just buying a subplate from Chick.

[Geof]

Originally Posted by Donkey Hotey .....The subplate won't be used for anything other than holding the Chick vises, so fastener clearance won't be a consideration for other setups....

I guess I missed that these are vise mounting plates. We have several machines equipped with two or three Kurt Duolocks on plates dowelled to the table slots and we get longitudinal positioning by put a 0.500" pin in a tool holder in the spindle and bringing the edge of the fixed jaw up to this. Our repeatability is about +/-0.001" which is fine for us.

Regarding your oddball jaws are they dowelled to the vise jaws? There is no provision for this on Kurts, the alignment just comes from the 1/2" bolts which have about .01" clearance. All our oddball jaws all have reference holes in them to get the final precise work zero position.

[RICHARD ZASTROW]

Greg, a jig bore reamer is not a jig borer (machine). The jig bore reamer is supposed to bore/ream an existing hole undersized hole in an accurate/precise location. In my day,(the old days to you) the really accurate/precise machines were jig borers, hence the name "jig bore reamers".

A well built geometrically correct machine with a new fangled gadget called a digital read-out (DRO) more or less made them obsolete. Jig borers are still in use today though.

Oh well, I 'spose that's progress. LOL

Dick Z

[Donkey Hotey]

Originally Posted by Geof Regarding your oddball jaws are they dowelled to the vise jaws?

I guess you haven't played with Chick vises. They use a pretty ingenious design. I think they handle soft jaws better than the Kurt design but they may sacrifice some rigidity in the process.

I have the older M-Series vises which use pins to retain the moving jaws. Chick has moved on to the System 5 series which are basically the same, but the moving jaws simply snap on or off.

To answer your question: the center jaws are completely removable (flush to the vise). They are located by round & diamond pins coaxially located around vertical SHCS holes. This Solidworks image will give you some idea where I'm heading and what the vises look like.

This shows the first vise removed and the 25mm fastener and pin spacing on the mounting plate. The silver blocks are consumable soft jaws. The center jaws are bolted to the vise base via the vertical counterbores you see here. The floating jaws are held by a floating pin in the horizontal holes. Each pin rides in a ramped slot on the clamping slide within the vise. It provides the same kind of down & forward action of a Kurt vise.



I originally intended to do 50mm spacing but upon looking at the different vises, I found that only the 6" models have the cross-axis locating pins. The only locations that the 4 and 6" models share are the 250mm longitudinal pins. Because I'd like to mix & match vises, I'm now at 25mm spacing for both dowels and fasteners.

Unfortunately, there is no edge distance for inserts anymore. I'm glad that I'm designing my own. The turnkey Chick subplate wouldn't allow the tight grouping that I'm going to get out of my own design.

[JWB_Machining]

I'm not offering any help here, only aksing more questions. What are these dowels you guys are speaking of? I'm having trouble understanding all that. I have Vise keys and I love them because then I don't have to spend time squaring up my vise, at least for the accuracy I need at this point in time, but are these dowels you speak of more repeatable and accurate for making your vise square? Also Since I have Donkey and Geof's attention, I use a Kurt 6" vise on a TM-1 and my keys fit into the T slots but as I slide the vise in the X direction the keys tend to get snug at a certain spot Table? Is this something I should be conerned with? Do I want the Keys in the Snug spot or the less snug locations?

Sorry if I'm de-railing the topic Donkey.

[Geof]

Originally Posted by JWB_Machining ...I use a Kurt 6" vise on a TM-1 and my keys fit into the T slots but as I slide the vise in the X direction the keys tend to get snug at a certain spot Table? Is this something I should be conerned with? Do I want the Keys in the Snug spot or the less snug locations? Sorry if I'm de-railing the topic Donkey.

This tight spot loose spot thing is why I mentioned in an earlier post that the alignment precision from keys in the Tee slot is around 0.0005". The keys have to slide in the tight spots so they have clearance at the loose spots. All that is affected is the alignment but only by a small amount.

[Metal1cutter]

Accurate hole location on a CNC mill with a saddle holding the table on top of the "Y" axis.

If the table position is extreem to the left, then most of the weight will be on the left "y" axis way. The weight on the right "Y" axis way will be light. So during a "Y" axis movement the saddle will tend to twist toward the left. The amount of twist will depend on the amount of running clearance in the "Y" axis.

So! To prevent that, always center the table, to balance it, on the saddle before you move the "Y" axis. This is extra work, but it will pay off in performance.

The next thing I suggest is use one "Round" dowel pin and one "Diamond' pin in the vise body for location. The round pin will locate the vise position, the diamond pin will locate the rotation to the square position. This will get you what you want with the added advantage of the vises being easily removable.

Best regards,

Stan-