Centring a mold cavity in the mill.

[firebyprolong]

Let me start by saying I'm kinda green at running my mill effectively. Most of my experience has been on the lathe. I have a couple of molds that I'm planning on cutting for a hp pin. I'm shooting for a larger Lyman type spud because it's pretty straight forward, just a little larger so that I have the ability to modify the nose shape and the cavity dimensions. Only issue I'm having is centering the cavity. Can I get away with just using a kick out wobble center finder on the base of the cavity? Or do I need to indicate off the sides of the cavity using a plug gauge and center with a dial indicator in the quill. I can see how both would work just look for suggestions before I go to hacking away. Thanks

[bob208]

use the indicator n the base of the mold. just like indicating n any other hole.

[country gent]

Remove the sprue plate and screws. I have seen a piece of cigarette paper placed between the blocks also but may not be necessary. Set blocks up in vise on a good set of parallels. First indicate the top flat with a finger indicator. May take a little tapping to get dead zero on the top. ( this should get the cavity parallel to the spindle). Next indicate the cavity it self in to zero. This needs to be done by not using the parting lines in the X axis. Get it to 0-0-0-0 and lock table in both axisis and recheck it didn't shift. Should be good to go. Another trick is to use a piece of round stock between moveable jaws and blocks, this helps allow the blocks to seat and square to the solid jaw better. Also make sure all burrs are removed

[white eagle]

use an edgefinder that how I would have done it
there must be 100 ways to skin a cat

[firebyprolong]

Thanks guys, I'm getting better about set up at this point but still have some major learning to do. I wanted to make sure I wasn't looking at this sideways. It looks like I need to invest in a last word and an edge finder set. I always found it kinda humbling that you can look at project make a plan and get results only to have a experienced machinist take one look at it and show you a much simpler, faster and easier way to get more accurate results.

[country gent]

Get the 3/8" and 1/2" round edge finders with the double ends and one end .200 dia. The old style "wigglers" work but arn't near as handy. If your going to use it just in the mill an intrepid with back dial and the swing mount is easier to read than the front dial ( when on the back side the dial is pointing at the column and is hard to read or requires a mirror). Starret made one with a dial the swiveled from front to back also. .001 is fine with more travel than the .0005 or .0001s have. These are handy for several things squaring or tramming the head, truing the vise parallel to the table, indicating holes and edges or finding centers. There is a mount that is a double jointed swivel that is very handy in the mill. Goes in a 3/8" collet and clamps to the dovetail on the indicator. If all you work in is Steel ( magnetic materials) a corner finder ( Chair) is nice. put it on a corner indicate hole in and both edges are found. More commonly used on jig borers and jig grinders but works nice in the mill.
For what you want to do indicating the blocks square and then the cavity in is the easiest way. other wise you need to measure out the cavity from 2 edges. or work down in a small cavity and take play out of threads.

With experience comes the short cuts and set up tricks. After 35 years as a tool and die maker I'm still learning. Another trick for thin springy things. Double faced tape on a flat milled plate is a life saver.

[Wayne Smith]

PM Buckshot. He probably has more experience with non-squared molds that anyone other than Eric!

[akajun]

Ditch the edge finder, this is indicator territory. Get an Indicol Mount and a Mit .0005 long stem indicator so you can reach deep inside the mould.
Another thing to look out for, squareness of the outside of the blocks to the cavity. This could have been caused by the factory, warpage of the blocks over the years, and dents and dings to the blocks.

I check for this by putting the tightest fitting gauge pin in the blocks I can, centering on it in the vise at the end closest to the blocks, then moving the quill up and down to see which way I need to tap it to get it as close to square as possible. You may find that it is out one axis more than the other if so turn that good axis to the jaws and tap the bad axis true in the open axis. If their both bad you may need to shim.
Lastly when you get it as close as you like, indicate it in again off the deepest driving band you can.

[dkf]

I use one of these https://www.mscdirect.com/product/details/06451512 and a test indicator. They make different sizes, have to make sure you get the right one. A coaxial indicator will do too. An edge finder is not accurate enough for a good job.

[firebyprolong]

I have a couple of blocks that I set up and ran into the "block really not square" issue. I do keep a bunch dismantled fealer gauges to use as shims in my toolbox. I'm shopping around right now for an indicator and will probably have to mount it in the collet for a while. At this point my budget only allows for used tooling so I'm gonna have to shop around used. I'll be in Wichita this weekend so I might stop by "the yard" and see if I get lucky. One more question, can I get away with buying used name brand indicators or do I just need to bite the bullet and spend the money on new?

[country gent]

Check the local pawn shops as used machinist tools seem to make there way there quite often. On the finger indicators if used for measuring from blocks check the ball for flat spots worn on it. Also check it for being sticky as this can be a problem indicating parts in. Look for intrepids ( very good and dependable) Browne and Sharp. Also very good Starrett and Federal these usually have a reversing lever on the side making for a little trickier use. Starrett used to make an attachment for a plunger indicator to do holes that worked pretty well also. These indicators can be found used ( Pawn shops, garage sales, gun shows, flea markets). Starrett also made a finger indicator with a dial that swiveled thru 90* allowing for top dial 45* dial or back dial depending on use, made it easy to read almost everywhere. The front dials are fine in the lathe or for measuring from gage blocks basically where it indicator is stationary. when the indicator is turning to indicate in, the back dial is better. On a Bridgeport style mill a top dial is pointed at the column and hard to see. On a horizontal mill its pointed down, the back dial is always in easy sight. I have an old LS Starrett JR. that's a very early indicator works off the 10-1 ratio and pivot point. A small flat spring provides tension. Old and bigger but does a great job. Don't overlook the older tooling.

[country gent]

Sometimes a piece of 3/8" or 1/2" round stock between the move able jaw and part helps to seat the part square. If you have to shimm it definitely allows the part to sit better. This keeps the moveable jaw from over riding the fixed jaw and "pinching" it out of square. We did this when squaring stock up and when required. try to keep it close to center line of part when possible.