Author Topic: How do I machine a square hole?  (Read 11898 times)

Offline Mogas

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How do I machine a square hole?
« on: February 17, 2009, 04:00:40 AM »
Ok Madmodders
Thanks again for the welcome.
This is my first information seeking post so please excuse my ignorance!
Attached (hope I get that right) is a crude and unprofessional drawing of a locking tail-wheel for our kitplanes.
The standard tailwheel steering block does not break away and castor. I devised a cunning plan to modify it so that it will disconnect from the rudder and castor when deflected more than 30 degrees from centre.
This works very well but here is the problem: Everybody wants one!
I would like to do as much of this modification as possible with my lathe, the best I can do at the moment is drill the 5mm hole in the 16mm spindle but then have to file it square by hand, this is the time consuming part! particularly when I have about 10 to make  ::)
First prize for me would be if I could machine this square hole blind and not even have to weld and re-turn it.
I hope that this makes sense.
Tools I have are an ordinary lathe and drill press. I hope to have a small milling machine soon.
Any help would be greatly appreciated.
Mogas

Offline sbwhart

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Re: How do I machine a square hole?
« Reply #1 on: February 17, 2009, 04:46:39 AM »
Hi Mogas

Now this may sound a bit rough arse,  :whip: but one way you could do it is.

1:- Make a 5mm sqaure tool bit by modifying a bit of HSS, or file  one up from silver steel heat it to cherry red quench in water temper back to straw colour quench again.

2:- Drill your 5mm hole.

3:- Mount your 5mm square bit of steel in your drill chuck or tool post.

4:- Make shure everything is clamped up tight, and force the 5mm bit of square into the hole, this will cut a square for you.

I've used this method in bits of plate.

Have a few trial runs on scrap before you do it for real, try experimenting by putting slight releafe on the tool, or using your vice to squess the square into the work etc.

You didn't say what the material was you were trying to cut if its ally it should work like a dream steel a bit more dificult

Good luck

And have fun
 :wave:
Stew

PS There is nothing wrong with the drawing it communicated the mesage 1st class,  :thumbup: you should see some of our Crap O cads we post.

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

bogstandard

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Re: How do I machine a square hole?
« Reply #2 on: February 17, 2009, 05:08:28 AM »
Hi Mogas,

Just a little note to let everyone know that this isn't a site where anyone can get free development time.

This site is run for hobbyists, and as such is not into bulk production problems.

But just in case you are a hobbyist just trying to solve a problem, this might help a little.

Why the square pin?

If the nose is shaped correctly on a round pin, and the spring pressure is correct, it should automatically keep itself in an upright position whilst swinging the nose thru an arc. The problems arise if the recess it is fitting in has any straight sides, then the nose can tilt over, in which case you would require side guidance of the pin to keep it upright.

If you would require the pin to stay upright with the hole providing guidance, then the sketch below might be a possible solution for you. It can all be carried out with a drill press and lathe, plus a bit of filing on the pin nose.

You can easily develop it using a bit of scrap material, and once you have the correct sizes for the side holes (they shouldn't need to be very big), then it is just a matter of transferring it over to the original items.

P.S. the stabilising pin thru the main pin should be the same diameter as the small side holes, and the ends rounded over by hand to fit the small side grooves formed. Also, you wouldn't need to drill all the way thru, then weld it up, as you won't need to file the hole square

Hope this helps

John
« Last Edit: February 17, 2009, 05:10:24 AM by bogstandard »

Offline Mogas

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Re: How do I machine a square hole?
« Reply #3 on: February 17, 2009, 09:32:13 AM »
Thanks bogstandard and sbwhart
John, I do produce these things for a profit and I certainly was not trying to pull the wool over anyone's eyes! I suppose you could call this free development time but in my defence your Honour I have to point out that I am sharing my ideas at the same time. 
In all seriousness I will stop this right here with this post if the Moderators so desire.
That would be a great pity as I have already seen a partial solution to this problem in your post John and would like to take it to bits a little further.
Watching with interest
Mogas

Offline Bernd

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Re: How do I machine a square hole?
« Reply #4 on: February 17, 2009, 10:05:46 AM »
Mogas,

John has just given you a gentle nudge as to the purpose of this site.

That being said please continue.

Regards,
Bernd
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Offline Mogas

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Re: How do I machine a square hole?
« Reply #5 on: February 17, 2009, 11:38:55 AM »
Thanks Bernd, point taken. I will go on but the offer still stands to withdraw this topic should anyone not be happy with the circumstances by which it came about.
BTW this started out as my hobby and has grown into a small business (hardly production line stuff) which I am very proud of.
The spindle shaft that the square hole goes into is turned from mild steel. The pin should preferably be square as I need as much bearing surface as possible on the brass cam as well as the half circle in the rudder horn where it engages to lock the rudder horn movement to that of the spindle.
Bogstandard's suggestion about stabilizing pins has some merit and got me thinking about a variation on that. The engineering is getting very small for me (must still be huge for some of the modelers!) so I think I will work on a plan to have a round pin with a nose shaped like John drew but have some sort of stabilizing groove down one side and perhaps a pin or grub screw engaging the slot.
Mogas

Offline Mogas

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Re: How do I machine a square hole?
« Reply #6 on: February 17, 2009, 11:47:22 AM »
Oh yes Stew, I did try the heavy handed route but it did not work despite the various relief angles I used. It simply went cockeyed and ended up a mess.

Offline sbwhart

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Re: How do I machine a square hole?
« Reply #7 on: February 17, 2009, 11:59:52 AM »
Hi Mogas

Good try you never know until you've had a go  :headbang:

The only other thing I can suggest is doing it in stages.

If its not a blind hole you could do it with a broach. I've got some at home but as I'm not at home at the moment I can't post some photos, if you're not familiar with broaches you could try Google search.

Good Luck

 :wave:

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

bogstandard

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Re: How do I machine a square hole?
« Reply #8 on: February 17, 2009, 12:14:46 PM »
Mogas,

Don't get alarmed at my statement. It has to go in.

On other sites I have belonged to, some people were trying it on to get things developed free of charge.

Eventually when we asked them for a share in their royalties, they disappeared in a cloud of dust.

Your reply was what we were after, it shows you are genuine and not after making a quick buck at our expense.

The ones I was on about could most probably be linked into the multi million bracket.

Last year, I was even approached personally by a US government department to do some development work, but because I didn't have my workshop up and running, I couldn't help. But it was passed over to someone else in the know, and hopefully they got the help that was required.

So at times, some of the help that is requested can get a bit wierd.

You will find all sorts of solutions to problems. The best way is to pick the meat from each one and see if it does the job. Mine was just a fifteen minute think about, maybe not ideal, as I don't know the exact circumstances, but if it gives you an idea of how to carry on, great.

John
« Last Edit: February 17, 2009, 12:17:55 PM by bogstandard »

Offline Mogas

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Re: How do I machine a square hole?
« Reply #9 on: February 17, 2009, 12:23:50 PM »
Thank you Sir. I am now firmly repositioned in my comfort zone!
Stew, I had a quick look for a broache and after wading through some ladies stuff I saw what you were referring to. If I persevere with the square through hole this could well work. I will persue this once back in SA.
My day job as a flight engineer has me away from my machines more than I like. I am sitting in Lagos Nigeria, yesterday it was Luxembourg. The temperature difference has been about 35 degrees C!

Offline SPiN Racing

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Re: How do I machine a square hole?
« Reply #10 on: February 17, 2009, 05:21:08 PM »
Im a little fuzzy on the thing... so forgive me if I sound stupid LOL

In the Radio controlled aircraft I used to fly, I was doing pylon racing, pattern, and unlimited acrobatics.

For the tailwheel on the planes I flew, I usully ran the tailwheels (I ran two small ones side by side for stability of the assembly) with the vertical part bent out parallel to the rudder itself. I then actually ran a small pair of rubberbands from a hook on the rudder, to the "tiller" on the tailwheel. That allowed it to steer at low speeds and as speed increased it was less and less effective.

In the case of the block you have.. I think I understand the square shaft with the button sticking out...
If it were me.. and im understanding things correctly..

I would chuck a piece of rod, piano wire, drill rod, what have you.. in the lathe. Round the end of it.
Then I would drill the hole 90% deep.
Insert spring
Cut rounded bar short enough to compress the spring without binding, and then pop it into the hole.

Now.. granted.. I think I may be confused.. but thats what I would try.
SPiN Racing

bogstandard

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Re: How do I machine a square hole?
« Reply #11 on: February 17, 2009, 05:25:09 PM »
Spin,

Full sized, not models.

Bogs

Offline SPiN Racing

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Re: How do I machine a square hole?
« Reply #12 on: February 17, 2009, 05:49:38 PM »
He he he Yes I figure it was full sized.. 

But I was thinking that a round pin would be as effective to exert pressure to keep the tailwheel aligned, and only in the extreme angle where pressure increased would it actually deflect..
SPiN Racing

Offline John Stevenson

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Re: How do I machine a square hole?
« Reply #13 on: February 17, 2009, 05:52:14 PM »
Why not move the whole pin design up to the top of the block?
have a collar than clamps onto the spindle with an inverse shape of the cut away and then the pin can fit in a slotted collar round the outside and points inwards.

This way it doesn't weaken the spindle and the slotted collar can be milled to take the square key.

I can do a drawing if you can't follow it but that takes more time.

JS.
John Stevenson

Offline John Hill

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Re: How do I machine a square hole?
« Reply #14 on: February 17, 2009, 10:19:08 PM »
Ummm.... I was correctly identified as a 'bodger' on practically my first post here so with that in mind this is how I make square(ish) holes.

I first mark the corner and drill them with the smallest drill I have that will go through the thickness, I also mark the centre of the square (or rectangle) that is the point where diagonals cross and I drill another hole centred there and and large as I can up to the width of the required hole.  Then finish with a file though I assume the same process would be easy to finish with the piece of HSS tool steel as per the first(?) suggestion.
From the den of The Artful Bodger

Offline Divided he ad

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Re: How do I machine a square hole?
« Reply #15 on: February 19, 2009, 01:27:44 AM »
Quote
Ummm.... I was correctly identified as a 'bodger' on practically my first post here so with that in mind this is how I make square(ish) holes.
  Uh o!  Sorry John....  :(



Just as a thought..... Would a spring loaded ball bearing not do the trick?

Hard, rounded and unlikely to get jammed as it's a sphere?     

It would only be a case of correctly tensioning the spring.... Grubscrew from the rear?  Or just a spring that is the correct tension?


Just all I could think of.....

Good luck!



Ralph.
I know what I know and need to know more!!!

Offline John Hill

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Re: How do I machine a square hole?
« Reply #16 on: February 19, 2009, 02:40:11 AM »
Oh, there is no need to  be sorry Ralph. :beer:

In fact I am thinking of changing my ID to 'The Artful Bodger',  if you could see the stuff thrown under my bench you would understand! :ddb:
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Offline Divided he ad

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Re: How do I machine a square hole?
« Reply #17 on: February 19, 2009, 01:32:34 PM »
 :lol: 
Quote
In fact I am thinking of changing my ID to 'The Artful Bodger',
   



Can you change your ID without re-signing up??  I never tried!  You'll always just be plain ol' "bodger"  to me John   :)     :wave: 


Hasn't anyone got a thought as to the ball bearing approach?



Ralph.
I know what I know and need to know more!!!

bogstandard

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Re: How do I machine a square hole?
« Reply #18 on: February 19, 2009, 02:53:14 PM »
Ralph,

Methinks that would have been Mogas' first attempt.

The problem would be the required range of movement, and the 'breakaway' feature required. I would suspect a ball big enough to do the job couldn't be accomodated in the main shaft, and any smaller would just drop out of the hole because of the throw required.

My brain now hurts.


Bogs

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Re: How do I machine a square hole?
« Reply #19 on: February 19, 2009, 02:57:13 PM »
Ok John, furry m$77!


Now you go rest that brain  :)


Just wondered concider me re-directed  :thumbup:




Ralph.



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Kludge

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Re: How do I machine a square hole?
« Reply #20 on: February 19, 2009, 05:48:37 PM »
I've been sitting here watching this thread trying to remember the tailwheel assembly on one of the airplanes I flew.  I don't remember all the details but the wheel assembly was attached to the fuselage via two coil springs (one on each side) that helped keep it close to centered on TO and landing.  OTOH, if one wanted to turn while taxiing, it would break away with a ball detent (I think) that was tapered to each side of center and held centered via a spring and the aircraft's weight.  Once it was out of the detent, it could swivel 360o and still drop back into the detent.  I'd like to say this was on an SNJ but I'm definitely not going to swear to it.  I do remember it was non-steerable and there was no lock in the cockpit. 

I do remember my first flight in the beast when I pushed the rudder pedal while taxiing expecting the airplane to turn and the instructor yelling, "Brakes!  Brakes!  BRAKES!" before I remembered that the tailwheel was independent of the rudder.  Ah, the fun of round engines and tail draggers. :)

BEst regards,

Kludge

Offline Mogas

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Re: How do I machine a square hole?
« Reply #21 on: February 20, 2009, 07:10:28 AM »
Thank you for all the replies, here are 2 pictures of the wheel normal position and castering back 180 degrees.
Most have been helpfull and given me some ideas, some I have tried before and a couple I am fairly sure won't work. If you can spare the time, I would like to hear more of your idea JS.