# Welding fixture tables: deciding on hole size and spacing



## keeena (Dec 6, 2021)

I have a table which I plan on drilling fixture holes into (similar to what @jmkasunich did in this post) and had a couple questions about factors to consider related to the hole sizes and spacing.

Each measurement system has a smaller and larger config:
Metric: 16mm at 50mm spacing; 28mm at 100mm spacing
Bananas: 5/8" at 2" spacing; 1-1/8" at 4" spacing

In some cases I've seen some imperial tables feature metric holes (e.g. 16mm at 2" spacing).

My Q's:

Do commercially available fixturing tools work with either size class? Or is the tooling specific to the hole size? I realize things like dowel pins would need to be exact fit, but do dogs and the expanding ball-bearing types of fixture pins fit both inch and metric holes?


Does one hole size system (metric vs. inch) have better tooling availability?


What would go into deciding between the smaller vs. larger holes and spacing (other than the effort of drilling more/less holes)? Should the spacing match the table size? Are fixtures more generally available in the larger spacing or hole size? etc...


Is it worth considering a mix of bored and tapped holes?

My table top is 6'x4', 1" thick steel. I'm leaning towards metric holes and a multiple of the standard spacing for now; I figure I can drill the in-between holes in the future if need it.


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## jmkasunich (Dec 6, 2021)

keeena said:


> I have a table which I plan on drilling fixture holes into (similar to what @jmkasunich did in this post) and had a couple questions about factors to consider related to the hole sizes and spacing.
> 
> Each measurement system has a smaller and larger config:
> Metric: 16mm at 50mm spacing; 28mm at 100mm spacing
> ...


16mm is 0.6299", only 0.005" bigger than 5/8".  From my research, tooling intended for 16mm holes works in 5/8" holes, and vice-versa.  Although in theory a 16mm tool _might _not fit in a 5/8" hole if the hole is on the small side (drilled holes rarely are).  I chose 5/8" because the slightly smaller holes means a bit less wobble.  Plus it was easier to find a 5/8" rotabroach than a 16mm one. 

2" and 50mm (1.969") centers are close but not the same, and unlike the hole diameter that difference accumulates over multiple rows of holes.  I intend to make fixturing that uses the holes to hold things square and to size, so since I do mostly inch work, I chose an inch grid.  If you are only using the holes for clamping or squareness, not size, it doesn't matter.

28mm is 1.102", which is 0.023 smaller than 1-1/8".  So that tooling is not going to be interchangeable between inch and metric.  The bigger tooling and 4" (or 100mm) centers seem appropriate for big tables and big work.  Also that tooling seems to be a lot more expensive.  That is a decision you need to make based on the kind of work you will do.  Welding heavy structural stuff (4" pipes, 3/8" wall tubing, 8" I-beams, etc) means more clamp force is needed to hold stuff down.  I don't do that heavy stuff, 90% of my welding is 1/8" wall or less.  So the smaller, less expensive tooling makes sense for me.


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## Woods_Walker (Dec 9, 2021)

So just in case you haven't started yet...
I did essentially this same project last summer, using a piece of 40"x 54" 3/8" plate and a mag drill. I ended up doing 5/8" holes on 4" centers using a mag drill, and was really glad not to have tried for 2" centers simply because drilling that many holes is a royal PITA, and I wanted to make the holes as precise as possible, since many fixturing accessories won't fit if your holes are even 1/6th off-center (unless you go to small bolts, sacrificing that precision). I was able to hold my grid to within ~1mm using VERY careful and repeated grid measurements scribed directly into the tabletop with a carbide scribe. This is also pretty handy for roughly measuring stuff now that I'm done building the table.

As for other hole size and spacing considerations, 16mm fixtures will just baaarely fit in the 5/8" mag drill holes, and most fixture table accessories such as those from fireball tool, strong hand etc will fit 4" centers. 4" is also close enough together that you don't end up with "dead zones" where your fixture clamps can't reach. Those 5/8 fixture clamps hold very well!

I'll post pictures later once I have permissions.


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## ahazi (Dec 10, 2021)

keeena said:


> My Q's:
> 
> Is it worth considering a mix of bored and tapped holes?



I have a CertiFlat 24" x 48" table with 1/4" top and side plates. It is laser cut with 5/8" holes (not sure what the tolerance is) on 2" center. I love it as it is very useful for any welding work. I regret I did not order the version with alternating holes and threads as I think it can be more versatile.

Ariel


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## keeena (Dec 10, 2021)

Thanks for the comments so far guys. I haven't started the job yet; just recently scored a mag drill for the job but need to pickup an annular cutter once I settle on hole size. Speaking of that: you guys find that annular cutters are accurate enough to do the drilling in one shot? Or would you drill undersize and ream? Because drilling hundreds of holes once is not enough torture...   

I have seen some videos on the 'tube for hole-locating jig ideas and will certainly be doing something along those lines.


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## jmkasunich (Dec 10, 2021)

I used just the 5/8" annular cutter.

I made my clamps from these cheap Bessey bar clamps ($20 for four):








						BESSEY Clutch Clamp Set (4-Piece) GSCC4PK-C - The Home Depot
					

This special 4-Pack is a great way to expand your clamp collection, as you can never have too many clamps. Each 4-piece package contains 2 each of the 6 in. GSCC2.506 and 12 in. GSCC2.512 clamp. The BESSEY



					www.homedepot.com
				




I cut the fixed jaw off and welded on a 1" long slug cut from Home Depot 5/8" mild steel bar.  The bar measures between 0.610 and 0.615", but even though it is 0.010-0.015 undersize it still grabs just fine.  My top is 3/8" thick at the thinnest spot, if it was 1/4" I'd probably want a closer fit.  Some folks use shoulder screws since they have a very accurate diameter.  I wanted to build clamps this weekend so I used the stock I could get right away.  Also, shoulder screws are $3 each (or more) at McMaster, while I got a 48" length of 5/8 bar at the Depot for $16.  I made a dozen clamps and still have 2/3 of the bar left over for other tooling.

I had one of those cheap magnetic TIG torch holders.  the magnet didn't hold all that well, especially after it let go and fell on the floor and broke the ceramic magnet in half.  So I removed the magnet and its holder and welded a slug of the 5/8" rod to the bolt that used to hold the magnet.  Now I can stick the torch holder in any table hole (see below).


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## keeena (Dec 11, 2021)

You've made yourself a great set there! I was a little curious if using bolts (grade 8) would be a problem if not welded ideally (pre-heat/slow cool), but its just a clamp. I think your use of mild steel is a better bet.

Have you seen where someone modded clamping style c-clamps from HF by cutting the fixed jaw off and welding on a dowel? I realize the clamps are meh but works on a budget.


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