Drilling and tapping of a steel table.

[KeithB]

I have a steel welding table. The top is a 3/4" thick piece of medium carbon steel measuring 48" long and 40-3/4" wide . The frame is primarily 1-1/2" x 12 gauge square tubing, with four heavy duty metal wheels that allow it to be moved when needed.

I have always wanted to drill and tap a grid of holes on the top that could be used in conjunction with other hardware as a way to clamp things down, but up until recently I had no practical way to do so. The only way to hold things to the table top is to (a) use vise grips and C-clamps if you're within a few inches of the edge of the table, or (b) weld something to the table top and cut it back off later if you have to clamp something on the interior of the table.

A couple years ago we bought a medium size radial arm drill (48" arm, 12" column) and that was just what was needed for this project. The only trick was to get the table under the drill head.

As I looked at this project I knew it would be a lot of work, especially for someone with the health history and challenges I've been facing, but I also knew that if I broke this project down into several discrete steps I could accomplish each one w/o feeling overwhelmed.

I broke the project down into the following steps:

1. Accurately locate the holes on the table surface.

2. Get the table under the drill head.

3. Drill, chamfer, and tap the holes

It turns out I had to add several steps:

4. Cut the supporting frame loose from the top and reweld it into a better position.

5. Drill and tap the holes that couldn't be done in step 3.

The first thing I did was try to figure out the easiest way to accurately lay out a grid of holes. I decided that the holes should be on 2" centers. Since that would mean 480 holes in the 20 x 24 hole grid I did not want to use a scriber and center punch.

I decided to make a drill jig using a piece of 3" x 3/4" x 48" aluminum flat stock. I used a two vise setup to hold the bar straight on the mill table. My mill only has 30" of travel so I drilled and reamed as many holes as I could, then I moved the piece down and realigned it with an alignment spud mounted in the mill collet. This let me finish up the rest of the holes. Measurements taken to holes on either side of the "jump" show very close accuracy.

Drilling the bushing bar using a two vise setup on the manual mill.


Reaming the holes to 5/8" to match the drill bushing OD


I could only do about 2/3 of the holes so I had to move the bar to drill the remaining holes. I used an alignment stud I made to locate a hole to re-zero to drill the rest.


The alignment spud out of the collet


I bought a couple hardened drill bushings off eBay, the OD is 5/8" to match the holes in the bushing bar, the ID is 27/64", the tap drill size for a 1/2-13 thread.

I also made several drop-in alignment bushings. One has a 5/8" OD and a short 0.125" diameter pin. Another has the same OD but has a 0.125" diameter hole. These will be used to help layout the first holes. Two more bushings with a 5/8" diameter on one end and a 27/64" on the other will be used to pin the ends of the bushing bar to the corner holes in the table.

The tools used to layout the holes.


The first step was to lay out a scribed line parallel to one of the long edges of the plate. I tried to make sure it would be the right distance away so the line on the far side would be the same distance from the far edge. Then I layed out the position of the first end hole, again making sure it would center things up. I made a small punch mark and then drilled an 1/8" hole using a hand power drill. I dropped in the bushing with the 1/8 projection and went to the other end of the bar. The bushing with the 1/8" hole was dropped into the bar and an 1/8" hole was drilled through it into the table.

Now that there were two holes, one on either end of the table, it was time for a little plane geometry. I pinned the bar down on one end and using the bushing with an 1/8" hole (yes there was a reason for that size, it it the same diameter as the carbide tip on my scriber) I scribed an arc on the tabletop. I then moved the bar to the other end and scribed another arc. This was enough to be able to scribe a straight line parallel to the first line, but not enough to be sure the grid was square and not skewed. I calculated the diagonal distance across the corners and using a steel tape layed out the place where the lines crossed at the corners. When I measured the distance between the intersecting lines they were very close to the exact distance needed, and by judiciously "fudging" I was able to get two punch marks in the right place. After drilling 1/8" holes at each location I was able to pin the bar into any of the holes and have it line up with the other corner holes. This was enough to allow the bar to be pinned into place for drilling. On to step 2.

The bushing bar clamped in place ready to start drilling the corner holes


Drilling the initial 1/8 hole.

 

[KeithB]

In order to get the table under the drill head I needed to cut away some of the supporting structure under the table to clear the knee table on the drill, and I needed to make a track to raise the table up high enough to clear the base. (It was about 1/2" too narrow.)

A few minutes with a Sawzall and the frame members were easily cut away.

Cutting away the ends to clear the knee table on the drill press


I made a track using some 4" steel channel. I cut some short pieces to use to raise the track up, and I made some longer pieces to put at one end of each track to prevent it from accidentally flipping. The track pieces were cut to 8' (96") long. (The size wasn't picked as an accident; after this project is done they will become the sides of an unpowered roller conveyor.) The pieces were tack welded in places where it would be easy to cut back apart.

Welding the track made of 4" steel channel


The tracks in place on either side of the drill press base.


In order to get the table on to the track I used our foot-powered manual forklift. I had to lift the table from the short side, the forks barely made it to the balance point at the center of the table so I put a large C-clamp on the edge of the table and clamped it to one of the forks; this was enough to keep the table from tipping forward. I had to put the table on the tracks from the side.

Using the foot powered forklift to put the table on the tracks. Note the C-clamp holding the table to the back end of one fork.


Here is the table in place ready to be rolled under the drill head.


The lift has a capacity of 880 pounds, and from the effort involved I have to believe the table is at least a 750 pound plus load. It was good exercise to pump the foot pedal with my prosthetic in place of my recently amputated right foot.

Once the table was in the track I could roll it under the drill head and start drilling holes. I could only reach about 1/3 of the holes at a time. I drlled the first third at one end, then rolled the table closer to the column and did the middle third, then I had to take the table off the tracks and rotate it 180* and do the 1/3 at the other end.

I ran into a problem drilling the second row of holes in from the edges. The 1-1/2" square tubing frame under the table top was just in the wrong place. Instead of drilling through the flat side of the tubing the holes were running into the edge of the tubing, which broke several drills and made it impossible to tap. After realizing what was happening I just bypassed the second row and did all the other holes.

The first 2/3 of the holes drilled and tapped. Note that the right end of table hasn't been worked on yet.


Another shot 2/3 done.


After I had drilled, chamfered, and tapped all the holes I could I took the table off the track and flipped it upside down using an engine hoist/cherry picker. I had bought some forged lifting rings and with some lifting straps and the rings I was able to do things safely and relatively easily.

I cut the framework loose from the table, there were only 6 small welds. Then I cut the framework into four leg sections and relocated them closer to the outer edges of the table where the first row of holes would be in the center of the tubing, not the edge. I welded the sections back to the table top and made some tubing splices to weld into place.

The table on it's back, the four leg sections have been welded into place and splices put in to connect them.


Once finished with all the welding and grinding I flipped the table back upright and put it back on the tracks. I finished the job by redrilling and tapping the outer two rows of holes.

This job cost seven taps, broken or worn out, four drills which I had to resharpen several times, and several chamfering tools. (I finally had to use a chamfering tool with an indexable insert, the HSS ones I tried didn't last very long.)

This project occurred over a ten day period and probably required 60-80 hours labor.

 

[KeithB]

Epilogue

The first thing I did with the table was use it to help cut apart the tracks into individual pieces. The long pieces will become sides for a roller conveyor.

Then I made some visegrip type table clamps using some drill press clamps I bought at harbor freight. I made some slotted bases and welded the clamps to them. The clamps come with a threaded stud on the bottom to go through the slots of a small drill press; I cut them off flush with the bottom of the bases. I also took some flat aluminum scrap and made some 3/4" thick spacers that can be used to raise the clamps up higher for tall work.

Harbor Freight drill press clamps reworked.


I made eight of these, here is the first six.


I did this project for two reasons - to enhance the utility value and usefulness of our welding table, and to see if I could do it despite being a double amputee.

I have already used the table several times and yes it is handier to use, that goal is accomplished.

My physical condition puts me in the handicapped category, got the license plate to prove it. But I have never felt handicapped, I still have a few brain cells that work ok and I have been able to cope pretty well with what life has thrown at me.

Improvise, adapt, overcome.

 

[Jeff H]

I'm in utter awe!

Good machinists have been inspiring me all my life. The strategy, tactics, planning, managing of resources, creativity, logistical prowess and flat-out DRIVE to accomplish something leaves me.... inspired.

 

[smokeywolf]

That kind of precision, it falls within the specs of a very nice welding table or put it through a blanchard grinder and you'd have a pretty nifty optical table.
You may have a lot of hours invested in this project, but every time you put together a setup on that table it will put a smile on your face.

Very nice!

 

[CWLONGSHOT]

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[KeithB]

Thank you @smokeywolf. It's not just a welding table now, it's a place to breadboard hardware. I've got a hydraulic project in the queue. Be nice to be able to clamp down cylinders and valves and such. And I can clamp down loading presses and other reloading equipment.

Ironically since I moved the legs apart it will now roll under the drill head and clear the base so I no longer need the track. I plan to roll the table under the drill and use the top of it to support the channel pieces for the conveyor sides while I drill holes for the roller bearings. I already have a fixture made to do that, I'll post that when it happens.

 

[Ben]

I simply love it when a great plan comes together.
Great work, now enjoy the finished product.

Ben