I’m drilling a 5/8" hole grid in a steel welding table using a Fireball-style template and guide bushings. I’m indexing the template off the holes I already drilled, and the holes mostly appear to stack/line up under the template, but I’m having trouble getting some of the 5/8" locating pins to drop in cleanly.
Some holes look like they may be slightly off in certain directions when I try to insert the pin through the guide bushing/template and into the table. I’m worried I may be compounding a small alignment error as I move the template across the table.
Important detail: I have not deburred or chamfered the holes yet. The holes still have sharp edges/burrs from drilling, especially on some of the underside edges. I do have a 3/4" 90-degree 6-flute chatterless countersink/deburring bit that I was planning to use to break the edges.
Questions:
Before assuming the grid is misaligned, should I deburr/chamfer all the holes first and then re-check pin fit?
Can burrs or sharp edges alone cause 5/8" fixture pins to bind even if the actual hole location is okay?
For 5/8" holes in a welding table, how much chamfer is appropriate? Just a light edge break, or enough for the pin to start easily?
Should I deburr both top and underside of every hole before judging alignment?
If a hole is still tight after deburring, what is the right correction method — reamer, step bit, die grinder, or leave it alone?
When using this type of template, what’s the best practice to avoid drift as I move across the table? Two pins minimum, clamp the template every time, drill only certain holes first, etc.?
I’m trying to stop before I make the grid worse. I’d appreciate advice on how to tell the difference between burr-related pin binding and true hole-location error, and what the safest correction method is for holes that are only slightly tight.
Yes chamfer the top and bottom of the holes. The chamfer needs to be large enough that the ball on the tacking bolt won’t damage the edge of the hole. There’s no special depth that is required. I prefer the look of a deep chamfer myself. Chamfer the holes then check the fit. A taper reamer may be needed to further clean and straighten the holes. Try that first.
Wow a reply straight from the creator! Thanks! This is my first welding table ever. I think I already a large mistake by even using it since the flatness of the table itself isn’t good (good of course is relative and I need to go through and figure out how off each area might be with feeler gauges and a machinist level) and maybe the reason why I’m having the alignment issue. Based on what you’re seeing does it looks like I could make it work?
I chamfered all the top side holes and tested with 0.6250" inch pins and most holes wouldn’t accept the pins and tested with a 0.6240" inch pin. Is the taper reamer I should use a hand reamer? If, after chamfering the bottom side, I still have an alignment issue - could I use the last row as a new reference? I’m getting a little confused on how to correct for the misalignment and establish a x and y datum. I ordered an aluminum straight edge, but I’m not sure how useful this will be.
If I am understanding correctly you have .001 clearance on the pins, if so and the table is not very flat that means your holes may not be perpendicular to the top of the table. That alone will cause problems.
A user in this thread Why the drill template doesn't align at 90 degrees used precision pins to increase the accuracy of the drill guide. He used 2 of the below pins. Why did he use 16mm if that is 0.629921" which is larger than the nominal size of the hole 0.625"?
Because the particular template I chose was the Fireball FA16 model, which is indeed 16mm. Well, it’s REALLY close to 16mm, as I don’t have an inside micrometer, and calipers just don’t cut it for TRULY accurate measurements. I can write a novel about the nuances of the actual templates VS the pin sizes used in their fixtures, but I’m not going to waste my time.
Sorry for invading the post lol, but I am searching for a good countersink bit, I saw Jason recommending a 6-flute bit. But I didn’t find one here in Europe.
Could you please share the brand, maybe I can find it here.
Built a measurement system for checking hole-position drift on your 96⅜" × 48⅝" welding table (2" grid): pins in adjacent holes, inside-jaw caliper reading + 0.6245" (your mixed 0.6240/0.6250 pin average) = center-to-center distance.
Created hole-drift-measurements.xlsx — 72 pre-planned measurements with auto-calculating error columns and color-coded thresholds (green ≤0.005", orange >0.005", red >0.010") — plus hole-grid-map.png labeling the coordinate system (R1C1 origin, rows R1–R23 along the short edge, columns C1–C6 drilled so far).
You measured all 72; we re-measured suspicious diagonals, caught one typo (D12), and produced hole-drift-analysis.png visualizing the patterns.
What we learned
The table is fundamentally good. ~70% of measurements are within ±0.005", there’s no runaway drift as you drill column after column, and the far corner (R22/R23) is square. Your process works.
Column C1 (your first column) is the one real problem. Its hole-to-hole pitch stretches +0.044" cumulatively over rows 1–6, and it bows toward C2 by ~0.017" through rows 5–12. Likely template registration settling in on the first column. Practical rule: don’t use C1 rows 5–12 as a fixturing datum.
Diagonal caliper readings are error-prone. First-pass diagonals showed a scary “skew” of up to 0.036" that vanished on careful re-measurement — the grid isn’t skewed. Lesson: any alarming reading gets re-measured before you believe it (your repeat measurements agree within ~0.003", so confirmed readings are trustworthy).
Going forward (C7–C47): after drilling each new column, take three quick verticals on it (top, middle, bottom). Catches a C1-style pitch stretch immediately instead of a column later.
