Mcwire 1.2 drill bits

This should be simple to answer if anyone has built a Mcwire 1.2...

Need some clarification from the documention [www.reprap.org]:

1) Which drill bit is the "x/x " drill bit below (for 3/4" thread cutting screws):

"Drill Pipes:
After you have made the indentations, ideally remove the pipes and take them to your drill press. If you do not have a drill press, keep them attached and get your power drill. You will want to drill through the pipes with a x/x" drill bit."

2) There is a '?' but is that the 3/16" drill bit (for 10-24 thread cutting screws):


"Drill PTFE Bearings:
Once you have all your PTFE bearings cut, you need to drill them out. This is pretty easy too. The stickers all have holes on them. Drill these holes out with the appropriate drill bit (3/16"?) When you're done, you can optionally remove all the stickers. They should come off the PTFE really easily. "

Thx

I found out using a tap-drill chart [www3.telus.net]

1) Which drill bit is the "x/x " drill bit below (for 3/4" thread cutting screws):
answer: use the #25 drill bit.

2) There is a '?' but is that the 3/16" drill bit (for 10-24 thread cutting screws):
answer: Zach said the 3/16" drill bit is fine, but according to that chart linked above and this other naval chart I have, the #25 drill bit is recommended for plastics (which is what the PTFE is).

If I'm looking at the guidelines right, you're looking for the correct hole size for a 5/16" thread cutting machine screw.

There's a guide on the following website for appropriate drill sizes for thread cutting screws. The top table is dedicated to metal.

[www.instockfasteners.com]

From the table, it would appear you would need a K size drill. Before committing to your final workpieces, I would recommend drilling holes through a couple of scrap pieces of the same material to check that the size is right.

I'm going to build my mcWire bot using ABS rather than steel piping. It should provide some interesting challenges when I come to mount the rails!

I hope someone here who has built one of these using the same materials will be able to help you further.

Hmm, confusing. But here's the mcmaster description for the screw [www.mcmaster.com] Funny that in the "part lister [parts.reprap.org] the "Self Tapping Screw 10-24 x 3/4" points us to the 1/2" version of the 10-24 screw. Oh well, I'm sure either length will work.

Anyway, the 5/16" machine screw you reference [www.mcmaster.com] isn't a self-tapping (or thread cutting) screw, which is needed for the pipe legs. So I think the 10-24 x 1/2" tapping screws are needed.

Thanks for the suggestion -- I'll make sure to do some practice drills on scrap. Show some pictures once you're done with your ABS Mcwire

Arthur Wrote:
-------------------------------------------------------
> Hmm, confusing. But here's the mcmaster
> description for the screw
> [www.mcmaster.com] Funny
> that in the "part lister [parts.reprap.org]
> the "Self Tapping Screw 10-24 x 3/4" points us to
> the 1/2" version of the 10-24 screw. Oh well, I'm
> sure either length will work.

The 10-24 self tapping screw lists a recommended drill size of #17 or #16.

#16 is 0.1770 inches
#17 is 0.1730 inches
3/16th is 0.1875 inches which is only 1/100th of an inch bigger.

Thanks John -- yeah I saw that mcmaster said the #16, #17 drill bits were industry accepted. But since it doesn't say which material it is for (different for plastics vs steel) I have reason to double-check (because I'm like that)

The base leg of the mcwire is made of steel. So according to this [www3.telus.net] , whose info mirrors this US Navy machining guide I have, we should be using a #20 (.1610") drill bit [I had stated earlier the the #25 (.1495") was the way to go, but that is for softer metals like Al, Cu, rather than the harder steel].

The concern with the larger drill bits is that the hole will be larger and may not provide enough metal for the threads to sink into. What I'm going to do is to be safe and experimental and heck, I'll try all the drill bits.

One hint from experience is if you twist off the head of the screw then the hole is too small. Start from the larger hole size and work down so that when you twist off the head you know that the last one was the right size.

I had to remove 4 different screw because they twisted off on me. Figured out the right size right after that.

---

Bob Teeter
"What Box?"

Bob, I don't get it. I think I'm missing some context. What do you mean by "if you twist off the head of the screw, then the whole is too small"?

The threads of the screw are designed to bite into the material that it is being screwed into. If the hole that you are trying to put the screw into is too small then the screw will seize up and snap off. Then you get the fun of removing the screw parts left and starting over. It's best to test so that you have the right size hole for the screw you are using in the material that you are trying to attach to.

---

Bob Teeter
"What Box?"

I get it. Thx bob.

This differs from what was recommended in the Mcwire instructions, but I just wanted to update the thread on my drill bit experience.

I drilled the pipe holes using the #18 drill bit. Tapping it using a tap wrench/guide, which is to say, I DIDN'T cut the threads with the self-tapping screws and you DID cut the threads using some dedicated tool like this [www.nolansupply.com] , it is probably best to use the #20 drill bit to create the hole. I used the #18 bit and tapped it and it was way too easy.

Btw, using the recommended self-tapping screws in #18 is already moderately challenging in Al, and impossible by hand in the steel pipe (or maybe I'm not very strong). I think a #17 drill bit would be nearly as hard. I guess that's why zach recommended using the 3/16" drill bit.

I probably "wasted" 2 hours messing around with this, but it was all in the name of good fun.