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Drilling/tapping long runs?

PFD402

Plastic
Joined
Jan 5, 2021
We are setting up to manufacture some custom machines that use linear rail and bearings in lengths up to 14’. The rails will mount to 1/8” wall steel tubing. We are trying to come up with the most effect jig for drilling and tapping the large amount of holes required to mount the rails. Currently, I’m thinking of a simple jig to locate the first hole, then use the rail it’s self and a transfer punch to mark the remaining holes. Any suggestions or better ideas to increase productivity? Thanks
 
We are setting up to manufacture some custom machines that use linear rail and bearings in lengths up to 14’. The rails will mount to 1/8” wall steel tubing. We are trying to come up with the most effect jig for drilling and tapping the large amount of holes required to mount the rails. Currently, I’m thinking of a simple jig to locate the first hole, then use the rail it’s self and a transfer punch to mark the remaining holes. Any suggestions or better ideas to increase productivity? Thanks

"We" need to understand the positional tolerances.....
 
14' The rails will mount to 1/8” wall steel tubing -> will need a solid straight base to be very true.

QT: [then use the rail it’s self and a transfer punch to mark the remaining holes.] with them/each numbered to allow for their manufacturing tolerances or placed in such a way to tolerate that error.
 
"We" need to understand the positional tolerances.....
.005-.010 every 4".

I can't think of a better way to do it. At least this way you know the holes in the tubing are going to match the holes in the rail.
That's kind of what I was figuring, but just making sure someone didn't have a better idea.

Just a thought.

Unless I've read it wrong - you aren't going to get many threads in 1/8'' thick material
The 1/8" wall thickness works fine, but thanks for checking.
 
If the holes are equally spaced I would mount a block on each end of a Bridgeport or long drill press table with a hole in each block just large enough for the tube to slide through. Then have a split block with the same through hole with three dowel pins. Two pins to locate the block halfs and one in the center of the hole in the top half of the split block to locate the next hole to be drilled. Mount the bottom of the split block the distance from the drill bit needed for hole spacing. Put outboard supports one each side of the table to support the long tubing. Then after drilling the first hole you can quickly orient the tubing for each succeeding hole by just sliding the tube and placing the split block halfs together.
 
You say you can be off by 0.005" or even 0.010" every 4". And people here are talking about using jigs with that 4" hole spacing to successively locate each hole. Have you given any thought what that could add up to in 14 feet.

14 feet = 168"

168" / 4" = 42

42 - 1 = 41

And 41 x 0.005" = 0.205"

And that is with your LOWER figure. It could be twice that at 0.010" per each 4".

I don't know what size screws you are using, but 0.2" is greater than half the diameter of a 3/8" bolt. Your hole would need to be made as a slot or with a diameter of 3/8" PLUS 0.205" or 0.580" to guarantee that the screws/bolts could be inserted over the entire 14 feet.

If you are using a #10 screw, the hole would be close to the size of the head or even larger, depending on the type of head used.

I am sorry, but you probably need that +/- 0.005" tolerance over the full 14 feet. Or at least +/- 0.010" over that distance. With that in mind, I do not like the idea of using a 4" jig to locate each hole in succession. Or, if you do, then it needs to be 4" +/- 0.0002" and that includes the slop when it is used. Even if you ream each hole, that is a tough nut to crack.

I would:

1. Try to make my first hole in the center. That way you can work both ways outward from it. Depending on your machine's requirements, this starter hole may possibly only need to be roughly located. Perhaps as much error as a quarter inch would be tolerable. But you must answer that question.

2. Use several jigs. The first one would locate on that center hole and have guides for two or three more on each side of it. This jig would be used for all of your rails and would be made with as much precision as needed, perhaps +/- 0.001" over it's whole length.

3. Then a second jig would be used for the next nine or ten holes on each side. It would have at least four pins in it so it will locate itself using the original center hole as well as three more on the one side and zero to three on the other side. This jig would be used on both sides of the center to bring the hole total to 5 + 9 + 9 or 23 total holes. This second jig would also be made to a tight tolerance, perhaps +/- 0.002" over it's full length.That would bring our total error to a maximum of +/- 0.005" over the center 23 holes.

4. Finally the second jig would be moved to locate itself on the outer 5 (or 7) holes made in step 3 and the remaining holes would be drilled. At most this would add an additional +/- 0.004" making our error total +/- 0.009" which is just under your original high figure for every four inches.

If the tolerances still add up to too much, you can tighten them up for the second jig and even for the first. If the same jig can be used for both the rails and the supporting frame under them, then you can probably loosen up the tolerances on both jigs a bit.

Part of the idea here is to use more than one hole to locate the second jig. That way, any errors in those holes used to locate it would be averaged out to a better figure than could be reached when using only one hole.

Of course, a nice CNC drilling machine with a 15 foot bed would be absolutely ideal.



.005-.010 every 4".

That's kind of what I was figuring, but just making sure someone didn't have a better idea.

The 1/8" wall thickness works fine, but thanks for checking.
 
The answer of "how" to do it changes a lot with:
Are you designing for your own manufacture? i.e. you have design authority and just have to make it so it works.
What QTY at a time?

If you don't have a drawing tolerance to meet, you can do this easily by hand, drill press, bridgeport or planer mill. Have a center drill ground so it fits nicely in the clearance hole in the rail. I have done this plenty and it is imperative to use a drill or centerdrill that is correct for the hole in the rail or you will have trouble with threads interfering with the clearance hole wall if your drill walks.
But a 14' long rail will not be perfectly straight. So up to you to clamp it straight.

If you have a drawing to meet you need to use a long machine with as few setups as possible.
 
I appreciate everyone's detailed replies! I like the idea using the center drill. I agree that making jigs may give me the most accurate repeatability, but starting off I'll only be making 6-10 of these per year. So, it seems using the rig as the jig would be most cost/time effective. Maybe it would be worth my time to check into the cost of having a machine shop with a large enough mill do them. I'll report back how it goes thanks
 
What is the tubing going on to keep it straight? how are you leveling/squaring the rails? Tube will have a natural camber and twist in it, are you counting on the rail to straighten the tube? The thicker wall hss shapes tend to have less bulge in the flats, which might be enough to keep the rails true enough. I can not imagine anything that is rigid enough with .120 (10 ga - tubes come in gauge below 3/16") wall would require a large external shape. Cold roll solid will save you more in headaches than the cost difference. Hot rolled and few passses with a draw file before layout would be better.
With only a few to make carefully laying out with a tape is better than a single reference jig. You do not get cumulative errors with this method.
 
Seems like a straight forward job to do and no real need for "increased productivity" given that you may only be doing 6 - 10 per year. I would buy some (42?) drill bushings that fit in the existing holes in the rail and drill a small hole after clamping the rail to the 1/8" wall tube. Just make a jig to align the rail with one end of the tube or jigs in both axis to aid in clamping.
Then I would remove the rail and use a drill/tap combo and hand drill/tap the holes which will be pretty easy in 1/8" material. Use a hand battery drill and practice on some scrap so you get the tap going straight in. Each tapped hole will take only seconds.
Set up the first rail and drill the holes then test each rail for alignment with those holes, if they all fit then good to go. If they don't all fit then you will have to drill and label each rail for its corresponding tube.
You will be able to do all of a years worth of these in your own shop for the cost of just one done by another shop and let us know when you have found a shop with a 14' milling machine bed.

Good luck,
Michael
 
I use drill taps all of the time at work and they are great. Usually get through 100-150 1/4-20 holes before snapping them. We used to have a plasma pierce to start on but now cut the drill size with our new laser.

Simply clamp the rail in several places, whack a snug hole transfer punch at each location, and drill away. I personally have a big box of 1/8" stub length split point drills that I use to start holes in pretty much anything I'm about to drill. If you have two people, one can go along with the stubby and the other guy follows with the tap. Just be sure to have enough of each.

Our shop has a laser and cutting square tubing is easy on any plate cutting machine if it's not too tall, so I might consider laying them out in cad and burning the holes in, but it sounds like a wash and not worth the laser time in this case.
 
Hole position tolerance build up is a very real problem with simple jigs working off the previously drilled hole or two.

I used such methods on my Bridgeport to put several sets of equally spaced holes in 9ft (8 holes) and 14 ft (12 holes) s respectively heavy rectangular tube for a weld up job, so tolerances were not tight, and ran into spacing troubles. Admittedly my jigging was a bit casual but I found that the errors were all one way so they added up.

Its possible that I didn't get the tube sufficiently level so the drill always walked in the same direction. Having to work with the tube pointing out the side door over the vegetable patch wasn't conductive to accurate levelling.

I suspect you'd get more accurate results working from the centre outwards and initially drilling every 3 rd or 4 th hole then coming back to fill in. Total error build up will be proportionate to the number of jigged steps so if you start by drilling only a few of the holes the total error should be less.

If I were doing any number Id seriously look at making up some sort of carrier for a mag drill and sacrificing one linear rail to use its holes as the locating jig for teh mag drill. Or do something similar balanced on the mill table with some sort of pin to pick up on the holes in the rail.

Clive
 








 
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