Rotary Table Alignment: Part III

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seal killer
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Rotary Table Alignment: Part III

Post by seal killer » Mon May 05, 2008 11:59 am

All--

After reading and thinking about all the advice and guidance I've received concerning alignment of my new rotary table, I assembled the following devices . . .
Image

Above: An R8-3/4" collet, a six inch piece of 3/4" steel rod, and an MT3-3/4" tool bit holder.

I put them together with the collet in the mill spindle and raised the knee being very careful to ensure that the end of the MT3 tool bit holder was inserted into the MT3 hole without touching any horizontal edge surfaces. The act of continuing to raise the knee until the MT3 tool bit holder was fully inserted pretty much centered the 118lb rotary table.

Image

Above: The assembly fully inserted into the MT3 hole in the rotary table. At this point, the rotary table axis and the mill spindle axis are probably pretty much aligned good enough for my purposes. But, wait! There's more!

I have that neat little BestTest DTI graduated in 0.0001" intervals. I had to use it! So, I built this little thingy . . .

Image

Above: Swivel joints, 3/8" steel rod, BestTest DTI.

I aligned like I tram the mill table: every 90* on the X and Y axis. The first time around, I discovered that after using my collet-MT3 assembly I was at the most 0.0008" out of alignment. I imagine this is plenty good for me, but I wanted to do better.

I was amazed by how tiny a force was necessary to move that big, 10" table one ten-thousandths of an inch! Plus, after all my concern, it proved very easy to do.

I would appreciate your criticism and guidance.

Thanks!

--Bill
You are what you write.

Jose Rivera
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Setting up RT

Post by Jose Rivera » Mon May 05, 2008 12:20 pm

Seal killer, what you're doing is OK for approximate center and rough work.

Indicating the outside is useless.

The outside of the plate means nothing!!

YOU MUST INDICATE THE CENTER HOLE. EITHER THE TAPER OF THE STRAIGHT PILOT HOLE.

As I mentioned before, that indicator is going to drive you crazy.
Get it withing .001" or .002" and not zero. You may never achieve zero with such sensitive indicator.

.002" will give .001" error in concentricity, enough for must work.

B.T.W., the pilot hole is that removable ring in the center of the table.
There are no problems, only solutions.
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seal killer
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Post by seal killer » Mon May 05, 2008 12:28 pm

Jose--

I can easily move back and indicate using the center hole (the pilot hole?). I will do that this afternoon.

More?

Thanks!

--Bill
You are what you write.

Jose Rivera
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Indicator

Post by Jose Rivera » Mon May 05, 2008 1:08 pm

On a previous posting I showed a picture of a indicator older with a micro adjusting screw.

You will be needing one like it or similar to speed things up.
With the one you're using is hard to do minute adjustments as one approaches concentricity since by hand one can move it to much or to little.

If you're going to be doing precise indicating on lots of holes, then put on you wish-list a coaxial: http://cgi.ebay.com/CO-AX-INDICATOR-MIL ... dZViewItem

For $40 "Buy Now" is almost like giving it away.

I don't have one of these, but my experience with China made indicators is that the quality is far more that what you paid for. They seem to produce nice stuff of more than acceptable quality.

Two digital calipers (6 and 4 inch) I bough from HF are as good as a Mitutoyo I have with the advantage that they turn themselves off and on automatically, on when they sense movement.

Two 1" indicators I also bought from HF are of more than acceptable quality.
There are no problems, only solutions.
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kapullen
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Post by kapullen » Mon May 05, 2008 2:43 pm

Bill,

If you indicate the table od, by rotating the table instead of the spindle it will let you know if it is a good referance.

If that runs true, then you can rotate the spindle to check center alignment of spindle with table.

It is good to know the relative concentricity of table od to center bore.

You may loose center with a job set up.

The readout may have a power fart, or a dial get loose and rotate.

Then you have to pull the job off to reindicate the center hole.

When indicating over slots, it is best to use only a couple thousanths travel (pressure) of the indicator.

You can lightly chamfer the slots as well.

Otherwise the indicator will be knocked out of position.

When indicating a "rough" surface like this, go all the way around and recheck your start point.

Kap
Fadal Turn, Fadal Vmc 15, Prototrak 16 x 30 Cnc Lathe, Pratt and Whitney 16 x 54 lathe, Pratt and Whitney Vertical Shaper, G & E 16" Shaper, B & O Electric turret lathe, 36" Doall band saw,
Enco B.P. Clone, Bridgeport CNC Mill, Delta 12" Surface Grinder.

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seal killer
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Post by seal killer » Mon May 05, 2008 4:03 pm

Jose and Kap--

Better?

Image

I indicated at four 90*s.

--Bill
You are what you write.

Jose Rivera
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Sort of in the dark

Post by Jose Rivera » Mon May 05, 2008 5:34 pm

I am sort of in the dark Bill.

In order to indicate the RT table concentric to the spindle, one most attack the indicator to the spindle, center the RT as close as possible to the center of rotation of the spindle, then with the indicator do the final centering rotating the spindle by hand.

This is only if you're going to use the center of the RT as you X, Y Zero, with or without a chuck.

Now, for checking TR run-out precision, then all you need to do is pick a point inside the hole and rotate the table to see how much it variates from zero in 360*.

You don't mention what is it that you're trying to do. Just playing?

Since you rigged some tooling to aid you on making the RT MT hole centered to the spindle using one of your R8 collets, then I have to assume that you're trying to make the RT concentric to the spindle with that indicator.

If that's the case, the indicator will be far more accurate than using a piece of extruded aluminum that is not even round. Mic it all around to see how much out of roundness it has.

Now, the outside surface of the Rot table is not considered a precision surface. Checking to see how much run-out it has should be only for reference, but the MT and the pilot holes are relative to bearing rotation and the mounting surfaces (horizontal or vertical).

As for buying a Coax Indicator, I don't have one though I would like to have one.
My mill may not have enough spindle to table clearance to justify buying one. The indicator method though crude in comparison to the coax, can do just as good or better job, just slower and more painful.

Now, the ring where you're touching with the indicator is removable and you'll have a secondary precision surface without it, or you can make a special ring if needed replacing the furnished one.

That hole is the one that you will use (with or without ring) to make a chuck backing plate. The backing plate in turn will have a step to center the chuck and tapped holes to hold the chuck secure.

The backing plate will have a loose-fit (.0005" to .0010") pilot nipple and four c"sunk holes to screw the backing plate to the rot. table after with four T nuts. (plus the chuck centering step)

The chuck will have three or four bolts that will secure the chuck to the to the backing plate's tapped holes, after the plate has been dropped into the hole with the nipple making it concentric to the RT and secured with the four c"ink screws.

Easy ah? :lol:

I hope I did not confused you to much :cry:

You need a lathe or pay someone to fit a chuck to you RT (mucho $$$).
Maybe you can buy the kit with the chuck from who sold you the RT.
There are no problems, only solutions.
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seal killer
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Post by seal killer » Mon May 05, 2008 6:38 pm

Jose--
Just playing?
Well, of course! This is a hobby! :) However, I am also learning a lot.

Here is my current goal . . .

I want to align the mill spindle axis with the rotary table axis and then move the rotary table, say, 1.50" + the cutter radius along either the X or Y axis. Then, I will plunge an end mill through a quarter-inch thick piece of aluminum and rotate the table until I have created a 3" diameter circle which I will then create a bolt hole circle within.

Of course, I might create the bolt circle first and then cut the circle out of the plate.

Eventually, I DO want to put a backing plate and a chuck--probably 4-jaw--on the rotary table. Phase II does sell the backing plate, chuck, and tailstock if I want one. (I do.)

My next significant robotics project will use the equipment and skills I am trying to develop now. I am going to create a four wheel drive, four wheel steering DC powered lawn tractor whose batteries are charged via an on-board motor/generator. The tractor will pull a gasoline powered mower deck and other accessories. All of this will be remote controlled with video supplied by a wireless camera mounted on the lawn tractor.

In other words, I will sit in my easy-chair in front of the big screen hanging on the wall above the fireplace and cut the grass.

Cool?

--Bill
ps The robotics aspect will be the fact that the lawn tractor will use several microcontrollers to do various things, plus there will eventually be a totally autonomous mode.
You are what you write.

Jose Rivera
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Robot

Post by Jose Rivera » Mon May 05, 2008 7:55 pm

Humm, sounds like a project that can take a year or more to perfect at retired speed mode :D
There are no problems, only solutions.
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seal killer
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Post by seal killer » Mon May 05, 2008 8:04 pm

Jose--

I never know how long a project will take since I have so many active hobbies. However, learning something about machining is number one on my list since it supports several of my other hobbies; robotics, shooting, the I-wanna-build-a-bike-someday hobby, and maybe others.

Oh, yeah. I forgot the chair-building business I want to start. I figure I can build these pre-WWII lawn chairs for about $125 and sell them for about $35. What could be better?

I just do not know where I am going to get the time for my "Bill's Bait, Beer, Barbeque, Bikes, Babes, and Beer" establishment.

Please continue to jump in there to correct and guide me.

--Bill
You are what you write.

Harold_V
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Re: Sort of in the dark

Post by Harold_V » Mon May 05, 2008 10:49 pm

Jose Rivera wrote:You need a lathe or pay someone to fit a chuck to you RT (mucho $$$).
Truth be told, an adapter plate can be easily machined with only a mill and the use of the rotab. The plate should be no less than 5/8 thick, and more is desirable. All depends on the height of the SHCS's used to secure the plate to the rotab. Aluminum is satisfactory for such an application, making machining easy! I'd recommend 6061-T6 as an alloy choice. 7075-T6 might be even better, but it's more expensive and you'd not realize any particular benefits. An alternate choice would be the use of aluminum tooling plate, which is very stable, and already parallel and flat. It comes from the mill already surfaced, with both faces papered to protect the finish. It is cast aluminum, not rolled, so it isn't as nice to machine, but would serve perfectly well for the intended purpose.

Using the mill, locate the four mounting holes that will be used for the plate, which should be larger in diameter than the chuck body diameter, to allow for the mounting bolts (SHCS's). The holes would be on a bolt circle greater than the body diameter of the intended chuck, allowing enough clearance for the heads of the screws, but within the OD of the rotab. Chuck size is limited in this case, and must be at least 1½" smaller in diameter than the rotab table diameter.

Drill and c'bore the four mounting holes, using the proper coordinates (using either A DRO, or properly applying the screws and dials).

Find center, and rough the center hole, leaving a .03" for finish boring. The center hole would accommodate a pin that is a snug slip fit with the center hole in the rotab.

Purpose for roughing the hole is to find center location of the plate for finishing the bore after both faces of the plate have been machined with a fly cutter to insure the plate is flat. The four mounting holes can be used to secure the plate for machining the top surface, but it may require the use of multiple clamps, moving them as required to kiss the bottom face.

Once both faces are parallel and flat, place the adapter back on the mill, dial in the roughed hole, and bore it to finish size. To accommodate long pieces, it's desirable that the locating plug be able to be removed when the plate is fastened to the rotab, so it might be to your advantage to design a plug that can't fall through the table, and is easy to grasp for removal.

After mounting the plate, which now has been faced, the bore taken to size, and a locating pin procured, you can carefully machine the plate to locate on the counterbore of the back side of the chuck you intend to use. The perimeter of the plate can also be machined once installed on the rotab, using an end mill. The plate should either be slightly larger in diameter than the rotab, to avoid hitting the table edge, or the plate can be mounted on thin parallels to provide needed clearance to avoid contacting the table with the end mill. A 45° chamfer can be machined on the edge using a 90° c'sink. Locate the mounting holes that match the tapped holes in the chuck, and counterbore them on the far side, to accommodate SHCS's.

The entire project can be accomplished without the use of a lathe----but it will require a little thought. The locating pin can be made on the mill, using a boring head to turn the needed diameters. If one diameter happens to be a common collet size, the part can then be gripped in a collet, with a lathe tool held in the vise. Using the head power feed, and either the table or saddle for feed, size is then easily controlled.

If all of this sounds like a lot of work, my, my! What a perfect excuse to procure that badly needed lathe! :-)

Harold

Jose Rivera
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BACKING PLATE

Post by Jose Rivera » Mon May 05, 2008 10:56 pm

No arguments here.

That could be really challenging job for Bill :D
:roll:
There are no problems, only solutions.
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Retired journeyman machinist and 3D CAD mechanical designer - hobbyist - grandpa

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