OK, I figured it'd be worth posting pictures of how our subplate turned-out. Thanks to all who offered advice as I was pondering what/how to do it.

The central area covers the limits of the XY work envelope. The areas on the left, right and front are outside the cutting envelope and used for utility clamping/locating.

The hole pattern in the center mimics the Stevens pattern --we wanted to be compatible in order to be able to purchase and use their workholding products.

The tooling holes were reamed direcly into aluminum and are a very tight fit to the Jergens pins we got. We took a week to test out various drilling/reaming processes to get consistent results.

1/2-13 holes are plugged with nylon setscrews. Tooling holes are plugged with rubber plugs from McMaster.

A total of 15 bolts hold it down to the t-slots. The plate is aligned in X/Y within one tenth of a thou (it took a very long time!). Truthfully, thermal expansion will probably negate that very quickly, but we thought we should go through the excercise at least once.

The center of the plate is flat to less than a thou. We ended up using a large (9 inch) fly-cutter for the center. The periphery is also very flat but I made no effort to make it match the center work area...it probably is within a thou or less of the center, but it isn't important. If I wanted to make the whole thing flat (and had to do it again) I'd custom make a large enough fly cutter to be able to cover the entire plate with it bolted down in home position.

The table and bottom of the suplate were cleaned, dried and coated with WD40 before mounting. We are going to remove it in about six months and see what it looks like.

We also took the time to make a few custom alignment tools to be able to get the plate back on with decent repeatability. We can get within about five thou of the desired center-aligned position very quickly (less than five minutes). Then you have to bolt it down lightly and tap it into position with a mallet.

-Martin

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A few more shots...

-Martin

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What were the advantages of reaming these holes over boring them?

I am not sure that there are any advantages other than reamers are cheaper?

We played with various drilling diameters --which changes how much material the reamer has to cut-- as well as things like lightly chamfering the holes to improve entry. We also tried interpolating the hole to a given diameter prior to reaming but choosing the right drill bit produced more consistent results.

We ended-up with center-drilling (#6) to about 0.425in followed by drilling with a 12.6mm drill (1.25in deep, 150RPM/F5.0), then chamfer lightly, 0.5000 ream at 150RPM/F5.0 in and out (1 in deep) and finish chamfer. This produced a hole that is a very, very snug fit to Jergens 0.5in tooling pins.

We tested about 50 insertion-extraction cycles with no apparent loosening (we wiped the pin with oil and cleaned it after each cycle). For what we have to do this is as near to perfection as we need to get. We wanted to see if we could avoid using press-fit bushings. For now it seems that we won't need them. We can always drill the holes out and press fit bushings later on. The plate has a couple of hundred tooling holes and they are consistently tight from the first to the last.

Next project is a vacuum clamping fixture.

-Martin

Boy thats a lot of holes.

If you didn't bore the holes then they are probably alittle out of position randomly.

I supose if your reammer was short enough it might tend to strainten out the drilled hole.

Normaly it just follws whats there.

Do you have the Renashaw Probes, for tool setting and part locating?

I'm always mounting to the table to gain max height.

But, I only have one VMC and need all the flexability I can get.

I normaly run two kurt reverse jaw vises and clamp any fixture plates in them. Probe the fixture for zero and run.

Years ago I had a MyCenter 3x 18x30 I think, and we had two kurt extra length vises. We could open to 24 in. and drop on 24 x 30 plus fixture plates.

We could clamp 24 x 30 jig plate. Although when we first did it the plate would hump up in the middle. So we made jaws that only gripped the top half of th plate so that it would force it down in the middle. We put a backing plate underneith to support it. We discovered the problem when making 18 up vacuum form molds and the molds in the middle were deeper.

I hope that plate works for you, but shouldn't you still indicate the fixtures you plop on to it. I don't trust the limit switches for homing on power up.

I would be checking Thermal growth moving your holes around and warping the plate and table underneith it. Might not be a problem but ABC ( Always Be Checking)

Wiz

Agreed on the hole locations. Drilling and reaming generally produces an on-size hole that's wherever the drill happened to make the hole. Short of a single point boring pass which is always the best method to establish true hole position prior to reaming, a light plunge cut with an endmill that leaves sufficient material for reaming can do a pretty good job of moving the drilled hole's center to where you think it is.

Re the home position and limit switches... Unless there's some basic problem with the machine, the home position should be the most repeatable position on the machine. The limit switches only tell the control to slow down and start looking for the encoder's index pulse, and that index pulse establishes your home position. Obviously, if there's any screw backlash, then the table position at home could vary within that backlash amount, but that would create problems with the true location of every position and not just home.

Old Monarch VMC's with GE controls had a settable parameter that would cause every G0 move to approach the XY location from the same direction so that the location was more dependent on screw accuracy and less influenced by machine hysteresis and other such factors. Obviously, it slowed the machine's overall operation somewhat, but according to the manuals it would increase positioning accuracy for jig boring type applications where cycle time generally isn't the main concern.

That subplate looks nice. Hopefully it works as good as it looks

The limit switches just get you close. They just tell the machine when to start looking at the encoder for position. Haven't you ever shut off the machine at night and powered back up the next morning and started running the same job?

Very nice job. On the only subplate I've ever made, we had slots milled in place for the vises. When we did remove it for a tall job (lol, we really did need that 1") it was as filthy, smelly, and gunked up as you can imagine. I had cleaned it up and oiled it before installing it too.
Again, very nice work.

Marposs. Same thing. You can see them in the pictures.

Yes, of course. Our programs will know where to go based on the grid location of the fixture. I am engraving that onto the table this weekend. With that in place it is a simple matter to call the probing programs and find where the blank is located.


Yup, we will. I took measurements off the machine's table before putting the plate on it. We'll take the plate off in a few months and measure again. If there's any warpage it should be obvious. If that's the case it is very likely that this plate will become modern art and we'll go out and buy a steel plate. It's a learning experience.

-Martin

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We checked a few holes after mounting the subplate and the worst case is about 0.0005in off from where it is supposed to be. We center drilled (about 0.4in deep) every hole prior to drilling. And drilling was done at a relatively slow feed in order to not force the bit into the material.

How much better would positional accuracy have been by boring rather than reaming?

I might just take the time to probe every hole and see how well we did.

-Martin

Thank you. It was a lot of work and and excellent CNC learning experience. I forced myself to write all the code by hand and not use CAMWorks. I used Excel for the calculations and then created one sheet for each setup that would take the numbers and generate the g-code for me. If anyone is interested in how this works I'd gladly upload the Excel file.

[QUOTE\When we did remove it [/QUOTE]

I wanted removal to be easy. We designed a rig that allows one person to remove the plate without having to hoist it at all. It just slides onto these rails and you can roll the entire rig with the subplate away. To put it back on you have to lift one edge about 1/8in to have it lay on the table and then push.

For quick alignment during installation we made a set of reference tools that very quickly get us within about five to ten thou (depending on whether or not you had your coffee in the morning!).

The whole idea was to make it easy to remove and put back on so we could do so on a regular basis and not wory about rust and crud accumulating.

If I had more experience I probably would have chosen to drill a set of alignment holes on the table for repeatable indexing of the subplate. I don't know enough yet to do something like that and not screw it up.

-Martin

Boring would have removed any error that your reamed hole has due to following the drilled hole position. Basicly, had you bored them the only positional error you would have in your holes would have been whatever your machine error is.

Nice work. I would probably have went with a water-resistant grease and a squeegee between the table and plate. It'll slow the coolant creep under the plate considerably. This creep is where bad things happen because it's slow, the anti-corrosive additives in the coolant get used up and rust results. The squeegee is because you only need a very, very thin film of grease between the plate and bed.

Understood.

Would you then even bother with center drilling? Probably not, right? Just drill, bore, ream and chamfer? For a 0.5in nominal hole, how much material would you have the boring tool remove? In other words, what size drill?

We did find that the countersink made a more repeatable hole if we chamfered the drilled hole a little prior to reaming. Must have something to do with the chamfer guiding the reamer into the hole a little better.

-Martin

Hello,

Nice job on your sub plate ! I made a simple aluminum plate for my Fadal and used Triflow (sp) oil on the table before mounting the plate. Never left the plate on for more than a few days and the startup of the black stains were present when removing the plate. You may want to try a short test to see what results you get. Lots a variables with coolant, oil, and I'm sure some electrolysis between the aluminum and machine table.

Brian

Let's dispell this notion of reaming once and for all.

After three decades of learning from the finest .....
Tool-makers
Gage & Fixture makers
Mold-Makers
In the area.

I have consistantly, consistantly, consistantly,
Had locational results equal to boring, by doing the following.

Spot.
Drill. THEN.
A sharp regrind end-mill, .006" to .008" below nominal. (reamer size).
Plunge to depth.

Then ream!! BUT not at the fine feed that is incorrectly taugtht.
Feed should be say enough to get about .008" per rev. per flute.
Minimum. MORE for softer alloys than for tool-steels.
Forget about 4-flute reamers at any diameter you can get 6 or more.

M1M

I remember "Half the speed, twice the feed" as a rule of thumb for HSS drills and reamers.

M1M, Agreed completely.
I have never been tought that way, I just figured it out because I hate boring heads to a point that I don't even own one anymore. I either ream with the spot-drill-endmill-ream combination or just interpolate the thing.


Martin, despite your hatred towards G-code and CNC controls, that looks to be a fine job!!!

Center drill if you use a standard HHS drill, not necessary with a carbide drill like Ford or Metal Removal. Then bore to size. NO REAM. And chamfer. It's 6061. You may have made it thru all your holes without an adjustment.

You could have just stopped and checked size on every 20th or 30th hole if you were worried about the boring tool holding size.

If your reamer held the + or -.0005 that the table checked to you should be fine. Sub-plate location holes are only to get you semi-close anyway. There is to much tol. stackup to consider this this kind of alignment super accurate. You have the sub-plate hole tol. and position tol., the pin OD tol., the mating fixture hole size tol. and position tol. .002 to .003 repeatablitaty at best. You can eliminate the pin OD tol. if you can use an expanding pin in your set ups.

Reamers may, under the correct conditions, produce posistional results some what like boreing. The intension of a reamer was never to correct position of a roughed hole but to hold consistant size over the life of the sharpening on the reamer. Where a single point boring tool is used correct any position error in the roughed hole.

Listen to the arguments. Reaming can be as good as boreing or go with the standard they are chasing, boreing.

Anyway, please report back once this is in service as to how the threads held up without inserts. I curious.

Now have some fun with this bad boy!

Don't have to love it to use it and make money with it! It's just another tool.

-Martin