Chamfers needed on back?

Fixture Tables
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I’m getting a 1/2” sheet of steel laser cut with 5/8” holes on a 2” grid. I wasn’t going to chamfer the edges of the holes, but am concerned that I might need them on the backside for the ball lock bolts. Do any of you have problems getting the ball lock bolts to tighten up with non chamfered holes on the bottom? I would think that chamfering would help but wouldn’t be completely necessary. Am I wrong?

Also, any ideas for a specific countersink bit to buy if I do? I’m finding lots of 3/4” bits but nothing bigger and not sure if that’s large enough.

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Yes is a good idea to chamfer the both sides of the hole. Any 90 degree chamfer bit works.

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Thanks Jason, but can you explain exactly what chamfering does (besides making it easier to install the pins on the front)

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you can find some larger ones here

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When the balls push out, instead of making contact with the sharp edge with little contact, they hit a flat surface with more contact. They will hold better.

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The sharp edge can damage or make an impression on the clamp pin or rod depending on clamp style. This will cause the clamp to not slide very well through the hole. Or worse the clamp will deform the hole. These scenarios depend on table thickness, hole to pin clearance, pin/rod and table hardness. Some clamps styles are to strong for the table top and cause hole distortion.

The tacking bolts like to have the chamfer to help retract the ball when you remove it from the hole. The chamfer also puts the load on an area that when the ball contacts the chamfer it distorts an area that won’t deform the hole ID. Also these cases are dependent on table material/ thickness and bolt design. Some bolts have 2,3,or 4 balls.

Overall is just good machining practice to put a small chamfer on the bottom.

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Heh Jason / everyone ,
I saw in one of you videos you chamfered with a hand drill, and I think I saw you use one of those little air tools that seem to be popular right now, which do you recommend? Until I saw you use the hand drill I had assumed I was gonna use the mag drill again with a Weldon chamfer bit. Any one else got a preference/ experience? I started cutting a 4 x 10 piece out of 10 x 10 sheet of 5/8” yesterday, slowly getting closer to haveing to sell kidney to buy me a fireball fixture tooling kit!:joy:

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I’d use a drill chamfer bit as my first choice. It’s much faster and has a better surface finish. Use the other air chamfer tool for the bottom and top plate edges. It’ leaves a more consistent chamfer than a grinder on longer surfaces. Then hit the edge with 220 grit on a orbital sander.

Here’s the chamfer tool for anyone wondering what I’m talking about.

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For the bottom I would use a mag drill (that chamfer is more important) for the top doing by hand is fine.

This is my opinion only

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Roger that , still a ways from that part of the build but want to have the bits on hand far when the opportunity finally arrives

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@Gringo.Ironworks
What’s your table size?

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4 x 8