The Home Machinist!

I make the T-NUTS for my machine out of aluminum, and machine them so the top of the T-NUT is only about .025 below the top surface of the table. I only have 3 inch vises so I seldom use anything larger than a 3/8 screw, that way, if there is a failure, I will strip the thread in the nut instead of damaging the table.

T-NUTS are easy to make. A busted out t-slot in the table is a bitch to replace.

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You can buy good parts, or you can buy cheap parts, but you can't buy good cheap parts.

The top and left edge are "picked up" (generally with an edge finder) and dials (or DRO) set at 0-0. From these two points you can locate features on (or in) the part. Wise people check with a scale before drilling holes, to ensure that no mistakes have been made. The top and left surfaces (think north and west) are a good choice, because they permit reading dials in the proper direction. Backlash must always be considered when turning the dial the opposite direction.

This is the method by which almost all work is accomplished by experienced machinists (assuming manual machinery). It eliminates the need to make layouts, as well as the need to center punch holes, a practice I find less than acceptable.

Tool and die makers tend to do some work with punched locations, often because they must match components that must be mounted. In such a case, transfer punches are a valuable asset.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Ok .. the first project in the book was ... to create Tnuts .. ahaha

as far as the edge finding goes .. here is my confusion ..

if you use an edge finder .. that is like 3/8 or 1/2 " .. and find an edge with it and
set your DRO to 0.

then you replace the edge finder with ANY tool that is of a different diameter .. it seems
to me that .. the FOUND edge is no longer valid ..

Hope that makes sense.

Most edge finders tips are .200, when it kicks out you are .100 from the edge.
Zero the dro then move the table .100 then re-zero and the spindle center line will be centered with the edge and you figure the cut by one half the tool cutters diameter.

Edge finders are made in a couple of different diameters.

I have a Bridgeport, which is .200" per revolution of the handwheel, so I use a .200" dia. Edge Finder.

I loosen the handwheel dial so that it is free to spin, then find the edge with the Edge Finder. Since the Edge Finder is .200" in dia. this means that the spindle axis is exactly .100" from the true edge of the part. I set the handwheel dial to .100, raise the quill, and turn the handwheel to "0" and the spindle axis will be exactly over the edge of the part. If you use the Edge Finder to pick up your X and Y reference point, the spindle will be axactly on "0,0" of your part. You then calculate your cutter diameter and compensate for te diameter of the cutter.

Edit: Oops, I lost the keyboard race to Jim, again!

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Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

It does make sense, but you should still get in the habit of making the two surfaces I referenced as your datum points. Parts almost always have dimensions that come from two edges, so keep them as 0-0 at all times. Make adjustments in the math involved for instances where cutter diameter gets involved. Otherwise the settings will be meaningless, having value only in one direction, with the loss of orientation with the reference points. That's never a good idea.

These are the kinds of issues that sort those that can, from those that can't. It's very easy to get confused. Minimize your confusion by not varying from this procedure.

A comment on using an edge finder. I typically run my manual BP---which has .200" travel per revolution of the handle. I use a .500" edge finder. When I pick up an edge, I set the dial to 150. I then know that 1¼ turns puts the dial at 0, and on the located edge. Resetting a dial can add error, so get in the habit of setting the dial, then repeating the edge find, to ensure that it happens where the dial is set.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

My edge finder is .200" so when I find the edge I just advance the the table .100" and zero the DRO.

Yea .. wow ..

I need a big brother bad ...

thanks

Don't forget to move the table .100 in the X and Y direction to allow for half the diameter of the edge finder.

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You can buy good parts, or you can buy cheap parts, but you can't buy good cheap parts.

Ok .. I know where I was thinking wrong. I was thinking that the edge finder was used
so that you could work on THAT edge.

After watching some videos .. I see that it is a reference for everything you do to that
piece. So .. if you need a hole located so far from that edge etc etc ...
you can reference to that edge. You can actually use the machine to locate
different feature requests on the piece.

Sometimes .. you have to hit me with a brick to get it ... but .. I finally do.

I hope it makes sense, to observe tooling offsets. Zero is always Zero, and X never marks 'the spot'.

After having set up on that edge, you are correct, a diferent tool will give a diferent -offset- from Zero for the tool path. Math for 3rd graders. Whether manual or CNC, tool size must be alowed for, or yo will under, or overcut the tool path. It is why I have a pad and pencil around to note diferent readings and targets. It is amazing how much confusion can rain in, and make you miss the mark.

IF you want to mill a 5" square, you cant just cut, run over 5" and get it right. You are cutting the center of the tool path. The tool will bring you in short. By adding one diameter of tool size, when you cut the path, half the tool dimension will disappear, on each end, leaving a true target dimension. Get it?

Like wise, once the edges are established, any other dimensions for layout can be applied with confidence as everything is in relationship to the '0' found edge. I hope you can easily see my meaning. Jus' tryina help.

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Big Dave

Be Alert! The world needs more Lerts.

And I appreciate it Dave ..

I'm actually getting confused again .. ahaha

If I find this edge by taking tool size etc into consideration ...
then .. I want to make an depression 3" in .. I can't just dial in 3" and mill.
the center of the depression will not be 3" .. the far edge of the depression will
be 3" ... right ?