alignment problem, please help

[djh82uk]

Hi guys

I have a problem, I need to make a 1.5 inch long "slot" down the center of a piece of round bar. But it is alway a little off centre, I will describe my process, please advise where im going wrong, im still a newbie so be gentle

i machine the round bar in my lathe to the desired diamter. I then move to my cnc Taig mill.

I have a milling vice with a V running down it's length that I use to hold round objects. Im not too sure how well the mill aligned, basially I have the bolts going into the T-slots, and then pull in it and tighten, I guess if the slots that the bolts go into are no precise, then neither is my alignment, but the problem is not withthe slot running down it's length, so can't be that bad, the problem is with it not being dead center horizontally, as in the cutter is not touching the highest part when it starts, it's not out by much, but enough to mess things up at 30,000 rpm (im making a spring loaded engraving tool).

Now then, one it's in the vice horizontally, I put the jog rate right down, put a 0.125 dia round bit (perfectly round, no teeth) in the collet, and slowly move it upto the side of the bar until i cannot see any light between where they touch, I zero the axis, move up the Z and move towards the center by half the diamter of the bit, I then move further to the center half the diamter of the workpiece. Now in theory i should be dead center, but im not, any ideas?

Im using a verner calliper to measure diamters which does not feel that accurate.


Also, un-related question, how the hell do I re-align a peice of round stock in my lathe chuck after taking it out and putting it back in, do i need to use a dial test indicator and turn it by hand until it moves, then tap with a small hammer/mallet?


Any advice appreciated.

DJH

[slink]

I WOULD FIRST PUT INTO V BLOCK WHICH IF IT IS NOT PERFECT THE LENGTH OF THE V HOLDING IT WILL CAUSE A PROBLEM , IN WHICH CASE I WOULD SHIM THE TWO ENDS OF THE V HOLDING AND THE ALIGN THE BAR WITH A .OOO1 INDICATOR, NEXT TO GET THE CENTER OF THE BAR INDICATE BOTH SIDES OF THE BAR ZERO ZERO NOT YOU ON CENTER , IF YOUR USING A BALL ENDMILL EITHEWR TAKE MAX. .010 DEEPTH OF CUT TIL YOUR AT DESIRED DEEPTH OR USE A REGULAR ENDMILL TO ROUGH OU THE THE BALL ENDMILL SINCE BALL ENDMILS DON'T TRACK WELL , YOU COULD ALSO USE EITHER UNDERE SIZE FIRST THEN INDICATE AND CHECK , THEN PUT IN ACTUAL SIZE AND DO TO DEEPTHA AND SIZE

[MrWild]

Use a dial indicator to find the center of the shaft and set your zero that way.

Or if you're just too poor to buy a $30 indicator, touch both the front and the back of the shaft. Touch front, zero, run to back of shaft and touch. Look at your reading (after taking out the play in your hand wheel) and divide that by two. This will be your center point.

I forgot to mention that your head absolutely needs to be trammed in to do these types of set ups. If the head is tilted, then the cutter will not be in the zero plane from the front to the top.

[djh82uk]

Thanks guys

well ive no idea how to tram the head, but it used to leave ridges when running a surfacing gcode, after adjustments I can still see the ridges but no longer feel them, so cannot be out by huge amounts for a hobby setup.

How do you do it with a dial test indicator? I presume to mean to find the top most part, but then how do I align the mill to the same point? I don't have any handwheel just cnc

DJH

[djh82uk]

well I just did one and it's 0.31mm out, I cut out an oval rectangle and then measured the height of the sides.

DJH

[Oldmanandhistoy]

Hi DJH,

Something like this might help.

http://cgi.ebay.co.uk/Centre-Finder-...QQcmdZViewItem

John

EDIT: better info on this link http://cgi.ebay.co.uk/STEEL-Centre-F...QQcmdZViewItem

[djh82uk]

thanks oldman, how would that help with what I am doing though? I can see it's a very useful tool nontheless, Im trying to work down the length of the bar (baer laying on it's side) and not on the end face, if ive gotten it wrong or confused please let me know, I still have so much to learn. I wish there was someone local to me who knew about this stuff.

ive just made another one, and was out by 0.3mm yet again, so here is what I was going to try, let me know if it is flawed.

I was going to get one of those edge finders that light up when they touch the edge (if I can find one small enough, my max collet is 10mm)

I was going to move it to the one side, touch, get machine co-ordinates, move to the other side, touch, get co-ordinates, zero axis, take the difference between to the side touches, divide by 2, and move that distance towards the center.

I think i could easily be out a few 10ths of a millimetere by doing it by eye.

anymore advice appreciated

DJH

[Oldmanandhistoy]

You’re milling a slot down the length of your bar?

Take a look at the other link I edited in; might make things clearer.

The tool can be used to centre your spindle over a round bar/tube laid horizontally.

Originally Posted by djh82uk I was going to move it to the one side, touch, get machine co-ordinates, move to the other side, touch, get co-ordinates, zero axis, take the difference between to the side touches, divide by 2, and move that distance towards the center.

Can’t think anything would be wrong with this method as long as you take into account the tool diameter.

[Oldmanandhistoy]

Originally Posted by djh82uk Also, un-related question, how the hell do I re-align a peice of round stock in my lathe chuck after taking it out and putting it back in, do i need to use a dial test indicator and turn it by hand until it moves, then tap with a small hammer/mallet?

Is this a three jaw chuck or four jaw? Self centring?

[rustamd]

find position of back jaw of vise(dont use the V in vise to hold the bar) than deduct half the thickness of bar, that should be your 0

[dapoling]

There are many ways to skin a cat to say the least.
If you want to do accurate work then you will need accurate tools, get a decent test indicator that reads .0005.
Dial in your vise then proceed to to dial in the rod along the X Axis and the along either front or back of rod and then along the top of the road.
Use an edge finder and pick up the center of the road and then you are set to go.

If you want to cut corners that is what you will get.

[djh82uk]

Originally Posted by Oldmanandhistoy You’re milling a slot down the length of your bar? Take a look at the other link I edited in; might make things clearer. The tool can be used to centre your spindle over a round bar/tube laid horizontally. Can’t think anything would be wrong with this method as long as you take into account the tool diameter.

Yes I also took into account the tool diamater, i am using 3.175mm tools in a 3.175mm collet, also double checked on my vernier calliper, so i just divide that by 2, aswell as the rod diamterer, then add the 2 halves together to tell me how much to move.

I have a dial test indicator that reads in 0.1mm increments

on another note it is a 3 jaw self centering chuck, came with the lathe so not going to be amazing quality (Sieg).

With regards not using the V in the vice, it is a small vice (50mm), and if I don't use the V then there is very little surface area to hold it.

I will look into that link you gave me.

Thanks

DJH