View Full Version : Drilling the gantry tubes and fixing the Y-Rails

Wed 18 April 2007, 09:32
Here is something I wrote for the ShopBotters - not all applies to MechMate:


The "drill" (pun intended) is as follows: (after welding the gantry)...... (deleted 2008-04-18)

1. Take a 2 lengths of .75x.25 flat bar, nearly as long as the rect. tube. Mark a good screw spacing off onto one of the flat bars, making sure to miss the redundant huge holes in the rails. Center punch the one strip only.

2. Clamp the second strip to the back of the first strip (vice grips) and drill 1/4" holes right through. Unclamp, reverse/flip the strips and see if all holes still line up. If they don't, you need to mark the strips for the position in which they will finally be used - top & bottom and end for end.

3. Using the strips as templates, clamp them to the rails and tubes. Measure from side to side for parallel rails, etc. - there isn't much room for error on a 5/16" screw through a 1/2" hole. First drill 1/4" holes in all of them. Lots of holes I know, but 1/4" is easy.

4. Enlarge the holes in the rails to 1/2" and enlarge the holes in the tubes to only 3/8" (keep the tube as strong as possible.

5. Enlarge the holes in the strips for the right tapping drill size (I havn't tapped a non-metric thread in 30 years, I can't remember the size) and tap 5/16UNC threads in the strips.

6. De-burr all holes. Maybe use a big flat bar to push/scrape through the rect tube? Degrease. Paint.

For installation:

7. Push flat bar into end of gantry tube (a slot must be left there for the motor wire connectors anyway). Let the flat bar lie on the bottom. Appease your gods now...

8. At each end of the gantry, drop a short (6") length of slightly sharpened 5/16UNC "full thread rod" (Allthread/readybar) through the top of the tube and "find" the corresponding threaded hole in the flat bar. Do at both ends, leavin rods standing proud on top.

9. Lower the rail over the rods and then lift the rods to bring the flat bar up to the top surface. Add more screws. Etc. Give thanks where thanks is due.....

Wed 18 April 2007, 17:10
For those of us that dislike using a tap, weld nuts attached to the 3/4" x 1/4" flat stock are a cheap answer.
www.fastenal.com (http://www.fastenal.com) Easy-Spot Weld fasteners (http://www.hpaulin.com/Catalogue/EasySpot.pdf)(6MB pdf)


Wed 18 April 2007, 23:14
Dislike taps??

Okay, maybe I did too, but then cordless drills came along. Granted, it took a few broken taps to get the right feel about 10 years ago, but it has become oh_so_easy to tap holes! http://www.mechmate.com/Forum/clipart/happy.gif

I still hate tapping blind holes, because that needs 3 taps. But, for through-tapping, we only use HSS spiral point machine taps - the ones used by industry in their automated tapping machines.

Tue 11 March 2008, 06:53
ok for industrial taps with my hand drill with 90 support it's quick an easy, to place the taped strips, the best i think is befor weld the gantry, put the first and the last bolts and after weld put the rail and fix it in center to hold the strip and after, rotate the rail and fix the other's bolts.

Thu 17 April 2008, 23:42
Hi Gerald, Just checking. in post #4 you say ...The "drill" (pun intended) is as follows: (after welding the gantry)......

Do I weld the gantry first then drill all the holes in the rectangular bar using the flat bar template. Or must I use my flat bar template to first drill the hole into the 100 x 50 rect. tubing then weld it together ? Thanks

Gerald D
Fri 18 April 2008, 01:51
Maybe you will see it if I make it bold:

The "drill" (pun intended) is as follows: (after welding the gantry)......


Fri 18 April 2008, 03:41
I was just confused...and that is very easy to do. Somewhere the instructions to weld the gantre states:

The notes on the drawing state:

1. Lay the two Cross Member Tubes 01 20 440 D across a firm workbench with the DRILLED HOLES AT THE BOTTOM. Clamp the tubes to the bench with 4 large g-clamps. (Construction starts upside down)

Now when do I drill the holes ? before or after welding the thing together?

Gerald D
Fri 18 April 2008, 04:01
You have caught me out - I have never done it myself :o
(my angle irons are plug welded to the tubes and the whole thing put into a big grinder to get everything parallel)

I don't think it makes much difference either way. Probably safest to do after welding in case the tubes end up out of parallel during the welding - but that is really impossible. Besides, there is adjustment space on the holes.

So, I am going to make the lazy (for me) choice . . . . drill before welding. That saves me from re-numbering the drawings :)

Sorry for inferring that you couldn't read too well :o- us Capeys have to irritate the Vaalies. :p

Fri 18 April 2008, 04:48
I'l do it MY WAY....sound familiar. I am a Vaalie by choice, born and bred in Vryheid Kwa Zulu Natal. So those comments run off my back like water of a duck's back. Groetnis

Fri 18 April 2008, 15:01

I drilled mine after welding, I just made sure that when I welded the assembly up, the seam in the rect tubing was on the bottom (non drilled) side.

ps what have we got here, a Shark in the Lions den - that sounds like trouble :) and by choice to make matters worse...

Gerald D
Fri 18 April 2008, 22:01
Good comment about the seam of the tube - I will add that to the drilling drawing. Thanks Alan.

Wed 07 January 2009, 19:44

I'm just hoping you can help me with an easy question...:confused: I notice that the 3/4" x 1/4" flat bar is drilled and tapped 5/16"-18-UNC and the rectangular tube is drilled through 3/8" to 1/2" diameter and the angle rail is drilled through 1/2" diameter. What is the reason for the rectangular tube and the angle rail to be drilled through with holes that are so much larger than the 5/16" screw? Is this to allow for future adjustment?

Thanks in advance for your help.:)


Gerald D
Wed 07 January 2009, 20:04
Yes, that is for future adjustment to get the rails precisely aligned parallel to each other.