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View Full Version : Making a long flat bar on a vertical mill



mikey553
08-18-2017, 01:09 PM
Let's say you have a piece of a long, uneven material, which you want to machine into a straight flat bar. It is much longer than your regular 6" vise can support. Think about a gib for a mill.

I have a 9x49 PM mill (Bridgeport clone), which I bought new some time ago. Sorry to say that, but the quality of parts and assembly sucks big time. I would never know that, but I was forced to take the mill apart to move it in the basement. Now I can see how crooked the gibs are, how bad are the adjusting screws. I may have to make a new gib or two in the future.

Now comes a question. Let's say your gib requires 24 x 1.6 x .6" bar to make it from and you obtained a somewhat bigger casting. How would you go about machining it to a nice, straight bar you can make the gib from? Long gib machining is a problem on its own, but for now let's concentrate on a material for it. I mean how would you support/clamp the casting for machining? I have some ideas, but would like to hear your opinions.

Mcgyver
08-18-2017, 02:07 PM
Let's say you have a piece of a long, uneven material, which you want to machine into a straight flat bar. It is much longer than your regular 6" vise can support. Think about a gib for a mill.

I have a 9x49 PM mill (Bridgeport clone), which I bought new some time ago. Sorry to say that, but the quality of parts and assembly sucks big time. I would never know that, but I was forced to take the mill apart to move it in the basement. Now I can see how crooked the gibs are, how bad are the adjusting screws. I may have to make a new gib or two in the future.

Now comes a question. Let's say your gib requires 24 x 1.6 x .6" bar to make it from and you obtained a somewhat bigger casting. How would you go about machining it to a nice, straight bar you can make the gib from? Long gib machining is a problem on its own, but for now let's concentrate on a material for it. I mean how would you support/clamp the casting for machining? I have some ideas, but would like to hear your opinions.

good question. tapered gib? I've done that several times, but never that long.

You could make a series of fixture blocks that bolt to the table, each with a different height you accurately space to hold the blank.....but I think I'd make an angle piece clamped in the vise and then walk the work along in steps. just for expediency - less custom tooling, if it get things done, is best. All the ones I've done get scraped afterward so milling it is roughing op

old mart
08-18-2017, 02:22 PM
I am in the fortunate position to have a couple of identical milling vices which I can set in line with about a 4" gap minimum between them. Even two or more unmatched vices could be fixed in line for a long job.
When I was aligning the vices, I found that the tee slot rear face was not exactly true to the X axis and succeeded in swinging the head of the drill mill sideways to completely skim the slot face which was about 3" longer each end than the X axis travel. The errors were about 0.005" in the table width and are now 0.001", good enough for government work.
I have a larger vice which opens much wider and runs in a different slot, but the errors with just one vice are not noticeable.

Toolguy
08-18-2017, 04:44 PM
I would clamp the ends to the table with the vise off the mill. This will allow milling between clamps. Mill the top side straight, parallel to the table top. Move the clamps inboard and finish the ends at the same height.

Turn the milled side facing down and put the old gib under the material and clamp the ends. Then you can make another cut parallel to the table and the new part will have exactly the right taper without doing any measuring or fiddly setups. Move the clamps inboard and finish the ends. You may want to reset the cutter height, as it may change depending on where the part is on the gib lengthwise. Just get the big end the size you want.

Of course if you have the gib out of the mill to do this, you will need the use of another mill. That may or may not be practical in your situation.

Mcgyver
08-18-2017, 05:13 PM
Turn the milled side facing down and put the old gib under the material and clamp the ends. .

I like that idea <thumbs up>

elf
08-18-2017, 05:49 PM
Support it slightly above a surface plate. Cast polyurethane around the bottom and up the sides enough to keep it in position. Mill the top. Remove the polyurethane casting. Mill the bottom and sides. Scrape to finish.

HWooldridge
08-18-2017, 07:34 PM
Can you fix the existing gibs? Have you blued them to see where the problem areas are? Might be easier to raise a series of dimples and refit it instead of making new ones.

Another suggestion might be to buy Bridgeport replacements and hand fit those.

tom_d
08-18-2017, 07:44 PM
I'm going to agree with "old mart" here and go with the two vice set up. They don't have to be a matched set, especially where you might need to add shims of some sort anyway to create a taper. Just get the two solid jaws in line and go from there.

Forrest Addy
08-18-2017, 08:17 PM
You guys are missing the obvious:

You have a turret mill featuring an expensive to make and fit turret and ram. The turret swivels and a ram extends allowing a wide area overwhich the spindle can be re-positioned without significantly affecting the vertical reference or the head tram. IOW, the object of the turret and ram is to position the spindle relative the the work over larger horizontal plane that afforded by the X - Y axis travels - without moving the work on the table. The plane of the turret joint and the axis of the ram travel are allegedly parallel to the X - Y plane. Clamp a large part on the table, work the area you can reach, re-position the turret and ram, re-reference a previous feature and continue. You can machine a work area nearly 2 ft x 4 ft using the turret and ram in coordination with the X - Y travels without moving the work. Naturally care muc be employed is continuing previously machined surfaces to avoid steps and laps.

Moving on to work too long for a single cut: Same deal. Holding long limber work to machine both side parallel or, in the case of a gib, tapered, requires a little thinking. Perform the face work with a finish allowance on the width. notch both edges to accept the corners of flat head screw heads (a small Woodruff cutter is perfect for the job.) Make a thick sub plate (I like a heavy wall rectangular tube) and machine it parallel.

Back to the work (gib.) Cut the edge notches in opposing pairs every ten thicknesses along the work's length. Drill and tap the subplate for flat head screws arranged so the heads tuck into the notches on both side to trap the width. When the screws are drawn up they hold the work flat to the sub plate. Take light cuts: this grip is insecure and easily disrupted. Want to cut a taper? Block up one end.

After the face work is done and rough fitted, machine the edges.

Machining gibs can be a pain if you've never done it before or don't have the fixturing.

A long mag table is an invaluable resource for making gibs. Flip it over and V notch the bottom for sine bar pins. They don't have to be an exact dimension apart, only parallel to the reference surface and to each other. Stamp the center distance on the side. After that, accurate angles and tapers are only a math problem away.

CalM
08-18-2017, 08:23 PM
Strap clamps right to the table. Shim as needed if tapered. Remove and reposition clamps as the cutter requires.

No magnets needed. ;-)

mikey553
08-18-2017, 08:32 PM
Thank you guys for ideas, but I am not ready yet to make a new gib. I am going to fix little things first and put the mill together. Maybe later I'll try to do something with gibs.

I was asking a generic question about how do you make a straight long bar out of the rough casting. I am sure people do it all the time, I just don't know the details.

Since the material is rough you cannot clamp it straight to the table or clamp in the vises without warping it. I do not have polyurethane components to mix and experiment with them and they are not cheap. How about using the side clamps right on the mill table or on the subplate? Mitee-Bite comes to mind here. We could use shims between casting and table in several places to provide some vertical support as well. Once two opposite flats are finished and the bar is still straight we can clamp it down to the table and mill 2 other sides with an end mill to get it close to the final gib size. The point here is to remove the casting scale from all sides and get the bar close to the final gib size before attempting to cut tapers. We may have to flip the bar a couple of times to minimize the amount of warpage.

I have never used any side clamps. Are Mitee-Bite clamps and similar ones any good? Any other ideas? I do remember that many years ago we used to have a big planer at work and we routinely cut big plates on it, reducing the thickness to the drawing spec. That machine could easily take 1/2" depth of cut and each curly chip was weighing about a pound. There were no top clamps since all top surface had to be machined in one setup.

Bridgeport replacement gibs are not the same as mine so it will not work. I did not try to blue my gibs yet, but looking at the overall mill assembly quality I have little hope. Matt at PM told me the machine was made in Taiwan, but I highly doubt that.

Forrest Addy
08-18-2017, 09:03 PM
It's not uncommon to machine a rough bar twice, Once to remove the "skin" and square it up and a second time, maybe a third to make it flat, straight, and to dimension.

I got a zillion stories about long skinny work where the forge shop, the fab shop, or the foundry barely left me machining stock.

boslab
08-18-2017, 09:30 PM
Bit of straight heavy bar stock, mill a slot to take the offending strip, drill a set of holes for grub screws, weld tabs on for tee head bolts, just a random thought.
Mark

becksmachine
08-19-2017, 01:30 AM
Long gib machining is a problem on its own, but for now let's concentrate on a material for it. I mean how would you support/clamp the casting for machining? I have some ideas, but would like to hear your opinions.

I didn't see where anyone offered an opinion about the material, or maybe it was just obvious to everyone but me. Just about anything other than steel would be my choice, well maybe not aluminum, but cast iron, bronze, even plastics would work with the suggestion below.



Back to the work (gib.) Cut the edge notches in opposing pairs every ten thicknesses along the work's length. Drill and tap the subplate for flat head screws arranged so the heads tuck into the notches on both side to trap the width. When the screws are drawn up they hold the work flat to the sub plate. Take light cuts: this grip is insecure and easily disrupted. Want to cut a taper? Block up one end.

After the face work is done and rough fitted, machine the edges.

Machining gibs can be a pain if you've never done it before or don't have the fixturing.

.

Another variation on this well thought out scheme would be to use the flat head screws in holes in the gib itself.

There would be no shame in having some through holes left in the gib as long as none of them are left exposed to drag swarf into the slide.

Just make the countersinks deep enough that the screw heads are below the finished surface.

Dave

Paul Alciatore
08-19-2017, 01:34 AM
How to hold it?

Standard clamps, tee nuts, studs, nuts, etc. You will need to elevate it off the milling table so use hard wood for spacers at first so it will conform to the irregularities of the casting. Clamp it from one side and mill the exposed edge and half the top. Move the clamps one by one to the side you just milled and then mill the second side and the other half of the top. That gets three sides roughly milled.

Now flip it over and switch to metal spacers to hold it off the table. Same clamping sequence: clamp on one side and mill the other. Then move the clamps and do the second side.

For a final set of cuts, do opposite sides, one side at a time. After doing the first two, rotate it 90 degrees and do the other two. That way all sides will be finished parallel to the opposite one and the thickness/width will be the same all along the length.

I have milled long panels and had to use variations of this technique. I found it convenient to obtain extra clamps in the small sizes that I used. I found that I could obtain extra clamps, step blocks, studs, tee nuts, and nuts to supplement the ones in a standard clamp set that I had bought. I recommend starting with a standard set and add more components as needed. The sets are priced substantially lower than the sum of the prices for the components in them. You can see some clamp sets here:

https://www.mscdirect.com/browse/tn/Clamping-Workholding-Positioning/Clamps-Clamping-Components/Clamping-Sets-Kits/Fixturing-Clamp-Sets?navid=12108431

This is not a recommendation, just an illustration of what I am talking about.

darryl
08-19-2017, 02:43 AM
You also have to consider how the material will warp when you machine it. If it's clamped solidly such that it won't warp, then you machine it, it could come out of the vises in a warped condition. Choice of material is important.

pinstripe
08-19-2017, 06:32 AM
Matt at PM told me the machine was made in Taiwan, but I highly doubt that.

Have a look at the electrical components. They should have their own labels. The Taiwanese machines I have seen use Taiwanese switches, contactors, motors, DROs, etc. Not proof, but it's a an indicator.

greystone
08-19-2017, 08:42 AM
A gib is an extreme example ...
but anything very long vs thick has the same issues of both warping after machining, and warping while using any rigid fixturing.

For a gib-type thing, .. perhaps ..
1. either floating clamps, allowing rigid fixturing
2. ferrobend etc. in a suitable base leaving very little volume needed.
U channel, packing perhaps, heat the stuff to 80C or so (less than boiling water), pour it in, wait 20 mins.

mikey553
08-21-2017, 09:32 AM
I appreciate your responses, especially the one about using heavy wall rectangular tubing for a sub-plate. Such sub-plate will make it easy to cut a proper taper for the gib as well. The suggestion about using multiple grub screws to hold the part on its sides seems to be good as well.

Still nobody replied about Mitee-Bite clamps. They are nothing more than eccentric screw running inside a brass holding block. I could probably make them by myself. Very easy to use, just don't know how effective they are.

vpt
08-21-2017, 09:37 AM
Glue it to a bigger piece of metal?

Illinoyance
08-21-2017, 02:50 PM
Strap clamps right to the table. Shim as needed if tapered. Remove and reposition clamps as the cutter requires.

No magnets needed. ;-)

Yes.
2 vises are easier if you have them.

Toolguy
08-21-2017, 05:41 PM
The Mitee-Bite clamps would work fine for this application.

CCWKen
08-21-2017, 06:50 PM
I would just double-sided tape or glue it to the table. Once the top side is flat, flip it over and do the same. Use the vise for the edges with the piece sandwiched between longer/heaver stock and clamp the ends too. Expose just enough to make your cuts. (I snatched that idea from a YT video.)

Danl
08-21-2017, 06:53 PM
Fields metal melts at low temperature. A long, narrow thick walled steel bar wide enough to mill a tub a little smaller than the gib, which could be clamped to the table. Shim up your gib-to-be in the tub slot, melt the Fields metal into the tub, leaving only the cast iron gib material sticking up. When done milling, melt out the low temp metal and reuse it on the next side of the gib being machined.

Might be cost prohibitive. Just a suggestion.

Dan

Peter S
08-21-2017, 08:33 PM
Still nobody replied about Mitee-Bite clamps. They are nothing more than eccentric screw running inside a brass holding block. I could probably make them by myself. Very easy to use, just don't know how effective they are.

I don't think they are "brass", more likely hardened steel and with a "gold" coating to reflect their price. I have used them for drilling jigs, haven't used them for milling, but that is what they are designed for I think.