Cutting Slots

[david pierce]

Tom,
There are numerous ways to figure out how to machine the slots in your plate. First, figure out the amount of precision that is needed in your finished part to establish the method of metal removal. Since bolt slots are a low precision endeavor, the layout process will work just fine.
1: Calculate the places on your drawing where you want the cutter centers then spray layout die on the plate and let it dry.
2: Loosely clamp the plate to parallels ( pieces of keystock will be fine) on the mill bed and indicate one of the edges on the X axis. This axis will be parallel to the long portion of your slots. When the plate is indicated in tighten your clamps. The parallels are there to
3: Mill the edge that was not indicated in parallel to the one that was.
4: Mill a Y axis edge perpindicular to the X axis. You not have X and Y datum lines to lay out your part.
5: With a set of digital calipers or a surface plate, angle plate and height gauge with a scriber tip, scribe the center lines of your slots on the X axis. Scribing in the slots is not necessary you only need the center line.
6: Reset your calipers and mark off the cutter centers from your Y axis datum. This will be the slot length minus 1/2 the cutter diameter on each end of the slot. Just make a short cross on these places.
7: Put a centering device in your mill spindle and line the center of the mill spindle over the cross mark. Zero in the Y axis dial then lock down the Y axis on your mill. The least expensive centering device is a wiggler.
8: Zero in the dial on the handwheel and crank the wiggler to the next cross mark of the slot. Make a note of the distance.
9: Remove the wiggler, put a cutter into the spindle and cut the slot between these distance marks.
10: If your need the slots a few thousandths wider than the cutter, after cutting through the plate, reset the Y axis by a couple of thousandths and take a couple of finish cuts.
david

[tmac1956]

david:

That’s helps a lot. I’ve drawn it out already, so the layout with the die and scriber shouldn’t be the too difficult. Using the actual mill will be the challenge… I’ll let you know how it turns out (or if I take my thumb of or something). I built some a wooden mock-up of the adjustment plates and they work ok, so at least I have the dimensions correct (it took a couple of attempts though). I’m going to order the plate already cut so I don’t have to suffer through hand sawing it, winding up un-square, and filing to try to fix it.

Thanks again!
Tom

[tmac1956]

david:

Here’s a really dumb question, but I’m accustomed to asking them so…

I have two end mill holders 3/16″ & 3/8″ dia. and a Jacobs chuck for small drill bits up to 1/4″. So, is the R8 collet set from Enco used for holding drills larger than 1/4″? I wouldn’t try to hold end mill cutters with those, correct?

Thanks!
Tom

[david pierce]

Tom,
Use the end mill holder to hold the end mill cutters whenever possible. The R-8 collets can also hold end mill cutters. Do not try to hold an endmill in a drill chuck as it cannot take the side force. Get some inexpensive CRS square or rectangular stock to use as parallels when milling through a plate. This will keep you from cutting into the milling bed when you cut through the plate.
david

[tmac1956]

David:

I have a set of parallels to use with the locking mill vise that you turned me on to. However, if the plate is too big for the vise, I’ll have to do that. I bought the clamping set from Enco too and I’ll try to find some key stock around town – the Harbor Freight store might have some. The last thing I want to do is to mill into the bed, so I’ll be very careful about that.

Thanks!
Tom

[david pierce]

Tom,
Nor do you want to mill into your precision paralles. If you place them judiciously under the plate to avoid the cutter you will be ok but it is always good to have some sacrificial parallels around. Do the T-Nuts in your clamping set fit into the T-Slots of your bed? Sometimes they stick in the bed slots and you have to file or grind the sides of the T-Nuts down a bit. Do not mill them as they are case hardened and will burn up your endmill cutter.
david

[tmac1956]

David:

I’ll test the T-Bolt fit with the slots first thing. Just looking at the clamping set, there looks to be a some variation (casting), so I’ll probably need to get out the files.

Thanks for pointing that out the issue about the parallels and the case hardened issue. I’ll have to be sure about the metals before I start cutting on them.

I can see I’ll enjoy this.

Thanks!
Tom

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