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Scotty M
01-17-2007, 10:59 PM
Hi, I'm new to using a rotary table and wanted to see if anyone had a good tip for the following. I have my table indicated in under the spindle and now need to center a small rectangular block. I need to mill a circular recess in this block and then add two milled slots at 45 degrees to the long axis of the block. I'm first stumped in getting the block centered in both axis, but then also in keeping one edge oriented so that I can start the two slots. I know this is done, but every time I get it indicated in in ane direction I lose it in another. Thanks for any advice.

mochinist
01-17-2007, 11:09 PM
If you have some scrap aluminum plate, or steel for that matter, you could clamp that to the top of you rotary table, set the table to 0deg's of course, lock it down and mill a small pocket that is a couple though over the size of your block, next just set your block in the pocket and use some clamps to hold it down and do what you need to do.

Nutter
01-17-2007, 11:10 PM
You'll want an Indicol style holder and a test indicator for this job. I'm not saying that it's impossible with a regular dial indicator, just that it's a lot easier with the right setup. A co-ax centering indicator combined with the test indicator and Indicol holder would make things go even faster.

Since your table is centered, you can start by drilling a hole in the center of the block. You are going to mill this away anyways. Then you can spin your test indicator with the spindle and measure the hole to see if it is centered (a co-ax indicator is also really nice for this). Leave the clamps part way tight so you can tap the block into position, then lock down and re-check. Turn your table 90 degrees and re-check if you aren't 100 positive you did it right, then turn it another 90 and re-check.

Make sure your dial or DRO is zeroed and then run the Y axis towards you until the block is clear of the indicator. Lock the spindle with the indicator stylus pointing forwards. Run the Y up until the block is touching the indicator. Then run the X back and forth and check for squareness just like you would when you are bolting down a vice. Use the rotary table to square it.

Remember that there is backlash in the rotary table and all the screws. Always approach your setting from the same side to take this out of the equation.

lane
01-17-2007, 11:10 PM
Tap litely

Benta
01-18-2007, 09:02 AM
Hi Scotty:
One of my machining books (don't remember which) gave me the following tip:

First: indicate the workpiece to the rotary table using an indicator on a magnetic holder. The rotary table should be fixed to the mill table. Unlock the scroll so you can rotate the table by hand and gently "knock" the workpiecce into place, then fully tighten the workpiece.

Second: indicate the workpiece to the spindle. Put and indicator into the spindle and rotate the table. Move X/Y-wise until it's centered.

I've done this myself, it's much easier and preciser than centering the rotaty table first and then trying to get the workpiece centered. Also, any errors do not accumulate.

Best Regards,

Benta.

Your Old Dog
01-18-2007, 09:13 AM
I made up a morse taper plug to fit into my rotary table. I then bored a blind 1/2 hole. I made up some indicators to drop into the hole. So, drop a spring in the hole, drop a 1/2" tool w/60 degree point into the hole. Put a similar tool into the mills chuck and line up the two points facing each other.

Now indicate on the bottom of your cube the center with a punch mark and position the punch mark on the cube over the spring loaded 60degree point sticking up from the rotary tables bit. Clam it down and have at it!

Let us know how you did it and how it worked. Pictures are always appreciated on this site if you are able to do it.

DISCLAIMER: I'm not a machinist so this is how I do it in my backyard amateur workshop and it's close enought for my needs. If I knew math better I might try a differant methode but I'm mentally challenged when it comes to math.........actually English language also.........and now that I think of it............. :D

BTW, notice you're a 1st time poster. Welcome to the forum. Where you from? Inspireing minds want to know!

JCHannum
01-18-2007, 12:18 PM
This is one of the advantages of a DRO. Once the RT is centered and set at zero degrees, the DRO can be zeroed and the table moved to half the cube's dimension. Fences can be clamped to the RT and indicated parallel to the two other axises (axii?), and used to locate the cube. The table is then returned to the zero location.

Lacking a DRO, the same procedure can be followed, but care must be taken to compensate for backlash. Dial indicators or other means can also be used to locate the zero position of the mill table.

Mcgyver
01-18-2007, 12:33 PM
I usually spot the hole locations in the vice using the x/y before mounting the rotary table on the mill. then once the table's indicated to the mill axis, I use the pointy end of an edge finder (with the mill stopped) to centre the hole in the block by moving the block and feeling when the the OD's on the edge finder line up. clamp carefully, checking as you go. an edge finder can be used without the mill running to a surprising degree of accuracy, provided it is decent and the OD's are the same. just do it by feeling when the OD's of point and barrel line up. this works on picking up an edge as well, i can get the results to a thou or two doing this as with the traditional method. to test how sensitive feel can be, do a blind test, take some gauge blocks in hand that are .001 different - it's not that hard to pick the larger one just by feel

Tinkerer
01-18-2007, 12:52 PM
I'd blue or black the part and scribe lines from corner to corner place a needle pointed probe in a collet and center the intersecting lines under the point and clamp down lightly spin table and check position. Then set up indicator if needed finer tuning. Or if is good enough tighten clamps and go to work.

pcarpenter
01-18-2007, 01:03 PM
I may be wrong as I am no professional, but it sounds like the rotary table is just complicating the job. A vice with a swivel base seems adequate to get the 45 degree slots done . The round recess sounds like a great application for a boring head.

But....maybe I don't understand the scenario. I don't even own a rotary table yet, but fully intend to make some plugs to aid in centering as already mentioned.

Paul