Fixture plate what size screws?

[Razzle]

I am building a fixture plate for my X2D minimill. Using 1/2" aluminum jig plate. The fixture plate will be 4" x 9". Trying to decide what screw size to make the holes. I am thinking either 10-32 or 1/4-20. My primary use will be to machine parts for model steam engines and eventually locomotives. So I want good hold down strength. Any opinions on which would be better? Yes I am making the hold downs as well.

 

[Alexander McGilton]

I would suggest 1/4-20 or M6, course threads as they're more resistant to cross threading. You can get small hold down kits fairly inexpensive, for the wook needed to mill all the slots and teeth.

I would be worried about those soft aluminum threads getting mangled in time and use. So you way well add steel threaded inserts in advance.

 

[kokoroko]

For machining parts for model steam engines and locomotives on your fixture plate, 10-32 screws would be ideal. They offer good hold-down strength and allow for more holes on your 4" x 9" plate, providing flexibility in setup and compatibility with smaller clamps and accessories.

 

[tq60]

If you buy a kit like above, thread to fit it so the hardware works

Sent from my SM-G781V using Tapatalk

 

[RaisedByWolves]

In aluminum I would want fine threads, so 10-32 or 1/4-28.

 

[GeneT45]

There are a couple of sizes, which if picked allow for a threaded hole that will snugly accept a dowel pin. I don't recall what they are off the top of my head, but it shouldn't be hard to figure out. An accomplished machinist showed me such a table that he made, and I've always meant to duplicate that idea if'n I ever get around to making a tooling plate. That might limit you to larger holes than are suitable for your application, but it's worth looking into.

GsT

 

[ChazzC]

I suggest look at the sizes of the parts that you will be holding: if most of them are going to be small, then 10-32 clamps are going to work better; but if the parts are going to be larger or require heavier cuts, the 1/4-20 would be best.

My LMS 3990 is basically the same size as your X2D, with a larger motor, belt drive and some other bells & whistles. I have a number of fixture plates:


The three at the top were cut from a 7" x 13" x 3/4" 6061 Sherline #3562 "Mill Tooling Plate" and have 10-32 holes and "Sherline" T-Slots that take 10-32 square nuts. The four on the lower right were cut from a 4" x 16" x 1/2" 6061 plate and have 1/4-20 holes. The one on the lower left is 6" x 8" x 1" Alca 5 (precision cast plate designed for fixture/tooling plates) and also has 1/4-20 holes. As I noted, I like the 10-32 hole plates for holding smaller parts since the clamps are also smaller. The 1/4-20 hole plates are more flexible since they have more holes and 1/4" clamps are available in a range of sizes.

I also have an SMW 6" x 14" x 0.60" 6061 plate that has 1/4-20 holes, and a Hobby Mod Vise to hold larger parts on the table:


The 1/4-20 holes in the SMW plate are countersunk for use with their Fixturing Pins for alignment (two of these pins are at the bottom of the photo above), which I think are what @GeneT45 was referring to.

I also have a number of Sherline angle plates that are 10-32 (and some with T-Slots) and other miscellaneous tooling plates that I have collected over the years.

Here is an example of using the Alca 5 plate, which is clamped using the outer jaws of my 3" milling vise:


The hand wheel is supported on the hub and the low point of the rim (on parallels); 1/4" toe clamps on the spokes & rim held the hand wheel in place for a light facing cut and drilling & tapping three mounting holes.

 

[Razzle]

I actually have two of the jig plates the same size so I guess I could do both screw sizes. I definitely like the fixture pin idea. I have seen that be really useful on some YouTube videos. I expect the plates to get chewed up over time. As for part size I think that won't be a problem for some time yet. I am not at the locomotive stage yet. So this build will be for smaller parts for the foreseeable future. I might need a bigger mill at that point anyway.

 

[ChazzC]

I definitely like the fixture pin idea. I have seen that be really useful on some YouTube videos.

The Sherline plates have 15/64" through holes in the bottom of the T-Slots which are reamed 0.250" halfway so that a 1/4" dowel pin can be used as a locating pin. This is much easier to do that making a precision countersunk hole.

 

[twhite]

I second the dowel pins and threads. Very handy to have both.
An example of use of pins. Very basic use but useful.

Cutting oil is my blood.