mcwire cartbot....drilling holes

I am working towards building a mcwire cartbot and I am having a terrible time drilling the holes in the iron pipe. The physical drilling goes well, but my holes are off center.

I can't for the life of me seem to figure out a way to get two holes in the center of the pipe.

Anybody have any ideas?

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Robert Carpenter
[www.robertcarpenter.net]

Make a small peening mark with a sharp Nail and a hammer or a peening tool,

Sometimes it's enough to use some duct tape to prevent the drillbit from slipping.

'sid

Get yourself a peening tool to mark the starts for your holes and deepen the peening dent a bit with a smaller diameter drill bit before you use your full-sized one. Also, make up some drill bit cooling solution out of a teaspoon of cooking oil, a teaspoon of dish soap mixed with water in an old empty plastic squeeze bottle (shampoo and dish soap bottles work best). Squeeze a little into the developing hole as you are drilling (Not at the same time, mind. Do stop your drill when you put in more coolant.) This will keep your drill bit cooler and it will both cut faster and stay sharp much, much longer.

Are you using a hand drill or a drill press?

Forgive my ignorance, but what is a "peening tool"? Is it the same as a centre punch?

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> Forgive my ignorance, but what is a "peening
> tool"? Is it the same as a centre punch?

Yup.

Corwin Wrote:
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> Are you using a hand drill or a drill press?

I have used a hand drill for most of my work. While, I have access to a heavy duty drill press with a cross-slide vise out at my sister's house in the country some 25 km away, until last weekend I did the majority of my drilling, mostly very small diameter bit work, with either a hand drill or my Dremel tool. I now own a drill press which mounts my Dremel tool. I use that coolant whenever I'm drilling metal regardless of which drill I'm using, however.

Edited 1 time(s). Last edit at 10/14/2008 12:30PM by Forrest Higgs.

Robert, et al,

First off, centerpunching the desired starting point should help prevent the drill bit from skating off. I find that a pilot hole around 1/8" (or 3 mm) is a good trade-off between drill sturdiness and amount of metal removed. They're also cheap if you bust one....

Having some sort of guide to keep the drill perpendicular to the pipe is key. To keep the pipe from rolling, support it in a vice (preferred) or with some scrap lumber with V notches cut into them. 2x4 is good for this (if you're in the US.) Note, for safety, position the pipe so the other end is touching something (other than you!), so that, if the bit catches, the pipe doesn't rotate and whack you a good one.

A drill press would be best, but I assume you don't have one. There are guides that attache to hand drills that only permit motion perpendicular to the bit.
Failing that, you might rig a guide using scrap lumber (or even some of your pipe.) I once saw a guy make the mating part of a guide out of styrafoam, carved to fit his drill, and duct-taped onto it, to keep the body of the drill steady and perpendicular, as he slid it along his ad-hoc guide. Crude, but it got the job done.

HTH,

Larry
ursine at gmail d0t c0m


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PS If you you have a vocational/technical high school in your area (or the equivalent), you might try asking the shop instructor, if they could help you out.

yea, I have a center punch...the problem is not the drill bit walking, it is my inability to locate the same center twice. I tried using the printout sticker that is on the mcwire howto page, but I couldn't even get close with that thing.

I drew up my own full-page sized paper sticker and that got me a lot closer. I think that my screws are setting at about 2

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Robert Carpenter
[www.robertcarpenter.net]

Robert,

I've never seen a McWire in person, so I don't know exactly what you mean by
"locate the same center twice" -- so plkease bear with me if the following is wildly irrelevant.

It sounds like you need (among other things) to make accurate lines on the pipe, parallel to the axis. (I'd suggest making only one line , and drilling straight through the far wall, rather than marking/drilling both sides separately. When you drill through (asuming you have a guide so you stay square to the pipe in both axes), the first hole guides the drill for the second puncture. Is the problem getting holes at 90 degrees from one another?

To get a nice line on the pipe, here are two suggestions that may work better than the taut string:

1. My combination square came with an attachment called a center head. (It looks like a wide V and slides onto the ruler part of the square such that the ruler bisects the V. See if you can borrow one. The centerhead can be used on the ends of a cylinder to draw true diameters. I think that, this could also be used, (with a scribe/pen and some tape to hold the scribe in place of the ruler) to draw a good line down a pipe. Put the pipe tight into a corner (e.g. desk agains a wall); brace the centerhead/scribe combo so the inside of the V runs on the pipe, and the outside of one leg of the V runs on one of your surfaces (e.g. table), and then slide either the pipe or the centerhead along the other.

2. Get a book (at least as thick as the pipe, preferably with thin, even pages. -- E.g. a phone book.)
Measure the pipe diameter. Put a scribe (or a thin, permanent marker) in the book, open to a page such that the tip of the scribe is at half the pipe's diameter from the table. Close the book on the scribe and have somebody hold it down (or clamp it. -- re-measure/adjust for compression, esp. if you clamp it hard.) Now, slide the pipe along the table and the scribe/pen. That should give you a good line to start from. Rotate the pipe so the first line is at the top, and repeat to get a second line at 90 degrees.

Yes, I meant motion parallel, bit perpendicular to the surface drilled.
Sometimes my fingers don't listen to my brain....

Especially when drilling steel (or cast iron) a *sharp* bit really helps, as does something harder than plain high-speed steel.
Even the import coated (TiN, TiC, etc.) drill sets (e.g. from HF or Enco) do a pretty good job. They're much cheaper than carbide (which is great, but pricy.)
Lastly, oversize holes/washers can cover up a multitude of sins -- though you then have to align all the parts within the range of motion that gives you.

HTH,

Larry

Well now I think I understand.. you drilled two holes, but they are not on the same centerline of the pipe , one is displaced...
Yes?

If so, let me tell you what my shop supervisor at the university used to say
"boy, if you can't hold a drill, try it with a saw!"

Well to be honest it was: "Stupid, if you cannot saw, drill it first" but that wont help here

What I intend to say is: If you don't succeed making two holes in one line, you'll surely be able to make two fine parallel cuts perpendicular to that line;
If you have a self tapping screw it'll do the rest for you

Afterwards you can (but you don't need to) close the rest of the slot with some dual component resin.

'sid

Made one, had the same problem. In the end I just marked approaximate spots, peened them, and then drilled the bastards straight through from one side. Got longer bolts and bolted them to my board. Same for the rails.

On the rails I leveled them out using shims and such between the many washers I used. Didn't take much, couple slips of paper and it was fine. Not as critical as you might thing initially.

Take a look here for pictures...
[objects.reprap.org]

Hope that helped.

Demented

robacarp Wrote:
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>
> That is an interesting formula for lube though, forrest.
>
> There are guides that attache to hand drills that
> only permit motion perpendicular to the bit.
>
Learned it from a guy who's forgotten more about machining than I'll ever hope to know.

It works well for drilling but it does make things rust. I now have a lathe with a compound slide which no longer rotates

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> It works well for drilling but it does make things
> rust. I now have a lathe with a compound slide
> which no longer rotates

You're supposed to wipe it off when you're finished!

I wiped it from the surface but it must have got inside the slide. To strip the slide down I have to remove a screw. To get at the screw I have to change the angle. The angle adjustment is seized, catch 22!

New lathe on its way hopefully.

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[www.hydraraptor.blogspot.com]

Bloody hell! I guess I never used the stuff where it could drip into the moving parts of a machine.

I'm a little confused about this whole question. This isn't unusual for me, of course, but I'll ask anyway.

Much simpler than a vise or etc. to hold the pipe is you just build the bottom part of the mcwire frame. With the pipes all screwed into one another and tightened in place, it's hard for them to move and you can sit on the other end of the frame if you need to.

Who cares if the hole isn't quite centered on the top of the pipe? Attach one end of each rail to one pipe, and when you drill the hole in the other end drill it through the rails and into the other pipe. It's not going to be perfectly centered in the exact top of the pipe, but I don't see as how that would make any difference. It won't move, and it doesn't need to be super accurate, so to hades with the rest.

It's only a 'strap anywho, as long as it prints workable parts it'll be fine, and 99% of the accuracy is in the steppers and threaded rods anyway. The only "accuracy" you need to worry about is:

1. Are the X and Y axies perfectly perpendicular? And skew will mean your machine draws a parrallelogram instead of a square.

2. Is the friction low enough that it doesn't come apart when driven by the steppers? yes? Then quit stressing about getting it perfect.

Some people might think that you need to worry about the table being level. You don't. What you need to worry about is the consistency of the height of the table under the tool head as the table moves around. But even that isn't important for the 'strap! You're going to be building a raft under your part, and the raft will eat any small inconsistencies in bed height. If you're planning on milling PCB's it's a different matter, of course, since the height MUST be consistent to within not much thicker than the copper layer on your PCB. That's where you get into minor shimming of the rail hight with a peice of paper on one end. But you can still shim it, no need to be to ultra precise in hole placement.

Now, *my* mcwire hasn't printed anything yet, so maybe I'm completely off base. But I did write "Hello World!" or a reasonable approximation thereof, so it's at least somewhat level. From my reading of Mr. McWire's original instructions, a large part of the point of the design is that the accuracy comes from having straight rails and threaded rod, so the construction doesn't have to be super accurate to get super accurate results.

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--
I'm building it with Baling Wire

... you can use pure oil as coolant too - so it wouldn't rust and it's no problem, when intruded somewhere ...

For releasing blocked/rusted metal parts you can apply frost-spray - maybe you can find it at the tool-store as nut-releaser or in medical as aid against strain ...

Viktor

Edited 1 time(s). Last edit at 10/15/2008 09:57AM by Viktor.

I have been using Trefolex cutting compund that Adrian recommended for tapping. It seems to work for drilling as well. It is green gunk with the consistancy of jelly so it doesn't run off.

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[www.hydraraptor.blogspot.com]

I had a similar issue. My solution:

1. Put the pipe on the workbench.
2. Jam two blocks of wood, of about half the height of and about the same length as the pipe, with edges known to be straight, on either side of the pipe.
3. Mark a line along the pipe on the top of one of the pieces of wood.
4. Measure along the line, mark position for holes.
5. Clamp pipe
6. Centre punch markings
7. Carefully drill
8. Realise when mounting the rails that Steps 1-7 could probably have been executed a good deal less carefully. Important: rails should be parallel. Important: rails should be fixed to pipe. Not that important: one rail being mounted 2mm off from the other. It's going to make attaching the motor supports very slightly trickier, but nothing that can't be fixed with 5 minutes and a round file.

Overall, having the thing now assembled, I've been impressed by what a forgiving machine the McWire is to build.

Thanks for all your help.

I was able to get my rails mounted. Documentation is here: [robertcarpenter.net]

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Robert Carpenter
[www.robertcarpenter.net]