Z-Plate hole layout and metric to inch conversion variance

[swatkins]

This post copied from another thread and edited to show Z-Slide Layout. http://www.mechmate.com/forums/showthread.php?p=37672&postcount=59

A variance in the plans for the Z-Plate when converting to inch from metric has caused a few problems for builders. Please note the spacing of the holes and do your layout carefully. If having these items made, make sure the persons doing the work knows these two pieces screw together.

Next up was laying out the holes...
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Because I don't have a CNC mill ( YET :D ) I still do things the old way... Layout ink and scribing the parts on a granite surface plate.

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One of my most used layout tools is an optical center punch.

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It's very simple to use and consists of a metal base with two precision holes. There is a hardened steel center punch and a plastic magnifying target that fits the holes in the base..

You first place one of the holes over your marked line. Insert the plastic target into the hole and look through the end.. You will see a small dot in the exact center. The plastic target rod is polished in such a way as it magnifies the target end and lets you see the fine scribe lines with ease... It also lets light in through the sides of the rod so that it is well lighted at the surface..

Once you have have the small dot over your scribe lines you hold the base firmly and remove the target rod. You then insert the center punch into that hole and give it a bam with a hammer.. Perfect alignment every time!

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Here is a shot of the plate after starting to center punch. (Drawing issue caught here) I caught a mistake here... I was a little confused on the drawing measurements and made one line too far over... I looked at the stiffener bar drawings and found the distance between the two rows of holes and corrected the layout before I drilled the plate...


And the finished plate and tube!

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My counter sink is not wanting to make the hole deep enough for the screw head to be flush. I think the holes are at the outer limit for this sink and the next size up is just too big... I tried using a drill bit to sink it deeper but there was too much chatter and the finish was not up to standards.. The screw heads are just a little proud so I might end up grinding them a little....

[Kart]

Just wanted to point out to those building an inch machine that 10 40 330 and 10 40 360 do not match on hole placement. I took these two to a machinist and they came back per plan. They could not be screwed together.
On the plate the holes are marked to be 1.2 " apart and on the stiffner one is marked 1.1".

[MetalHead]

Did they not catch to 30mm spacing that is also listed on the drawings? Also, did they know that the parts screw together? Did you loose alignment starting at the 4.1 inch holes?

[MetalHead]

You can correct this by re-welding the tube and make sure the holes align from the plate and redrill. You can also replace the tube piece. Work towards the tool steel plate since it is the harder of the two to fabricate.

[Gerald D]

The "mistake" on the drawing was to show the inches to one decimal place only.

The machinist shouldn't have calculated a pitch of 1.1 or 1.2 inches from only comparing a few dimensions. Pitch was never given. Both drawings have instances of of both 1.1 and 1.2 Strange that the machinist would look at two similar drawings and come to two different conclusions.

However, Kart's report should be taken to heart by all builders - be careful out there!

[tumutbound]

Another plus for the metric system :)

[bradm]

Surely you mean a cautionary tale about unit conversion ;)

I actually find it a potentially interesting story about the pitfalls of CNC or other automation in fabrication. If the two parts are fabricated together (a natural approach for a manual process), it is impossible to make the error. So this reinforces the lesson than CNC requires great attention to detail in the CAM process - which I've learned a few times after making revisions to parts to be cut on my MM.

[Kart]

I did tell them they hadto screw together. Maybe my saving grace. It's not the biggest of deals. A minor glitch in the scheme of things. It wouldn't have happened if I would have made it myself because I would hae used the plate as a pattern to the tube and ignored the the tube plan. Oh well, live and learn, learn, learn.:D

[Kart]

Did they not catch to 30mm spacing that is also listed on the drawings? Also, did they know that the parts screw together? Did you loose alignment starting at the 4.1 inch holes?

Yes, at the the 4.1.

[smreish]

...That small discrepancy not being noticed until now is most likely due to the build method recommends using the 100mm x plate as the layout and transferring to the stiffener.

I have built 3 machines and never noticed that...Of course, like Brad mentioned - I use the "manual" method on the first machine, then disassembled the slide to transfer punch the other two.

Thanks for the note. (I scribbled in my printed journal)

[JasonC]

Possibly a option of inch unit plans and metric unit plans be made available.

Jas

[MetalHead]

I have stuck this thread. This will make it stay at the top of the section for the Z-Slide

[MetalHead]

This is a great example of how tracking your builds in the forum and reporting things like this helps us learn new stuff and refine the build process for others.