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Old 02-01-2013, 04:13   #1
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Drilling Hole In S/s Square Tube Weakening Tube?

Hi I own a catamaran and need to install an autopilot ram which will attach to a box section of s/s tube which connects both rudders. This tube is 40mm x 40mm, thickness unknown. I want to drill a hole of approx 12mm in the centre of the tube through both sides to bolt the shaft of the ram drive.
My concern is will it significantly weaken the s/s shaft if I drill it?
I cant get a welder out to my boat around here as they dont seem to like to work on boats, so I am trying to find alternatives.
Any help would be appreciated.
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Old 02-01-2013, 04:22   #2
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Re: drilling hole in s/s square tube weakening tube?

A few pictures`would help,

I would suggest some method of clamping the Ram End to the tube thereby negating the need for any holes drilled.
But without a better look at your work site it's difficult to tell.

As a general rule i am not in favor of drilling through such a critical piece.


Quote:
Originally Posted by HueyHuey View Post
Hi I own a catamaran and need to install an autopilot ram which will attach to a box section of s/s tube which connects both rudders. This tube is 40mm x 40mm, thickness unknown. I want to drill a hole of approx 12mm in the centre of the tube through both sides to bolt the shaft of the ram drive.
My concern is will it significantly weaken the s/s shaft if I drill it?
I cant get a welder out to my boat around here as they dont seem to like to work on boats, so I am trying to find alternatives.
Any help would be appreciated.
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Old 02-01-2013, 06:33   #3
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Re: drilling hole in s/s square tube weakening tube?

Quote:
Originally Posted by HueyHuey View Post
Hi I own a catamaran and need to install an autopilot ram which will attach to a box section of s/s tube which connects both rudders. This tube is 40mm x 40mm, thickness unknown. I want to drill a hole of approx 12mm in the centre of the tube through both sides to bolt the shaft of the ram drive.
My concern is will it significantly weaken the s/s shaft if I drill it?
I cant get a welder out to my boat around here as they dont seem to like to work on boats, so I am trying to find alternatives.
Any help would be appreciated.
A 12mm hole in a 40mm SS box beam is not a problem at all.
Most cats have 40mm aluminum tubs that have holes drilled through them.
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Old 02-01-2013, 07:44   #4
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Re: drilling hole in s/s square tube weakening tube?

I dont think it would be a problem at all, plus its stainless steel its pretty strong, if you do drill I think cobalt bits are the only ones that will do the job easily, or at least make it easier. what about removing the tube and bringing it to a welder, or just fabricating a two piece bracket that clamps to the tube and has a eye for the ram?
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Old 02-01-2013, 18:38   #5
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This tube would be weakest in the center from any compression loads it may see. If you drill do it close to the end. If you need a hole in the center use a clamp.
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Old 03-01-2013, 12:07   #6
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Re: drilling hole in s/s square tube weakening tube?

Huey, I would suggest removing the bar and taking it ashore. Have the hole drilled with a drill press to ensure it is dead vertical. While a hole in the center of a beam that way doesn't weaken it tremendously, it should be fiarly simple to have a couple of extra plates or some extra L-stock welded into place to strengthen that area before drilling the hole.

Pehaps unnecessary, perhaps simply conservative, but as long as you are at the drill press, in a shop, why not add some reinforcing? that would also prevcent any wear from working the hole out, too.
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Old 03-01-2013, 12:29   #7
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Re: drilling hole in s/s square tube weakening tube?

Since it's a piece of tubing there are several methods for a strong hole.
1) If accessible, put a spacer inside the tube to clamp tight.
2) if not accessible, one can put thick washers the same diameter as the tube on the outside and clamp tight.
3) The best is to weld in an insert sleeve that extends out past the tube on each end to clamp tight.

If you not clamping tight then you should have the #3 option, otherwise the hole is going to elongate over time causing backlash and wear on the both the tube and bolt.

If it were mine I'd remove the tube and take it to a welder for #3.
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Old 03-01-2013, 12:47   #8
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Re: drilling hole in s/s square tube weakening tube?

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Originally Posted by delmarrey View Post
Since it's a piece of tubing there are several methods for a strong hole.
1) If accessible, put a spacer inside the tube to clamp tight.
2) if not accessible, one can put thick washers the same diameter as the tube on the outside and clamp tight.
3) The best is to weld in an insert sleeve that extends out past the tube on each end to clamp tight.

If you not clamping tight then you should have the #3 option, otherwise the hole is going to elongate over time causing backlash and wear on the both the tube and bolt.

If it were mine I'd remove the tube and take it to a welder for #3.

When drilling... slow rpm, once the bit starts to cut, keep it "in the cut" just enough to peel material out. Use a drill press. If your speed and feed is correct it will come out in nice spiral chips. as it starts to break thru back off a little or the bit will go thru early and create a messy hole. If your tube is thin wall, a 40mm hole is going to be a bit dicey to make nice. I'd take it out and take it to a pro unless you are experinecd.
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Old 04-01-2013, 21:15   #9
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If you want to do it proper. As a SS TIG WELDER I would drill the hole oversized enough to fit a tube with the inside diameter of the bolt and a min wall thickness of 1/8" you may need to have a machine shop make the sleeve for you. Then TIG weld it in the hole. You will not weeken the square tub that way. Just my two cents.
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Old 04-01-2013, 21:26   #10
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Re: drilling hole in s/s square tube weakening tube?

The only thing that can possibly work here is to have an engineer design a new arm for you and the have a machine shop cut one out of solid billet Monel with their CNC mill.
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Old 04-01-2013, 21:30   #11
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Re: drilling hole in s/s square tube weakening tube?

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The only thing that can possibly work here is to have an engineer design a new arm for you and the have a machine shop cut one out of solid billet Monel with their CNC mill.
A solid piece of SS 1-9/16" sq. would be so heavy and expensive.
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Old 04-01-2013, 23:57   #12
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Re: drilling hole in s/s square tube weakening tube?

You don't give us a lot of information on the use of this box section, however your concern of the weakening of the bar can be eaisly overcome as advised in the info already given by either
  • remove the bar and take to a land based shop
  • make a clampable sleeve outof suitable material with holes in the correct position so that you can simply drill out the section and the sleeve once clamped to the section will reinforce adequately with little loss in strength
  • make a sleeve that is clampable and offset a hole not through the section but beside it, leaving the section intact
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Old 05-01-2013, 10:28   #13
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Re: drilling hole in s/s square tube weakening tube?

It's all about the wall thickness, for drilling and for bearing area on the bolt that goes thru it. If it's not at least 1/8" thick I would have a tubular sleeve or at least a couple thick washers welded into or at the hole.
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Old 05-01-2013, 10:44   #14
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Re: drilling hole in s/s square tube weakening tube?

Drill baby Drill
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Old 05-01-2013, 10:45   #15
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Re: drilling hole in s/s square tube weakening tube?

Why can't the ram connect to the rudder arm vs. the square tube? Look closely at Cotemar's picture in the above post, the black ram attaching to the rudder arm. The problem with the tube is both flex and side to side movement as the rudder arms pull it fore and aft. It'll work on the tube, but the rudder arm is a much more positive connection to the steering system.
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