Drilling holes in stocks for the centres

discussion of the niceties of turning on a bow, bungee or pole lathe.

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Re: Drilling holes in stocks for the centres

Postby voodooalpaca » Mon May 28, 2012 10:18 am

Thanks guys,
I had a feeling self tap would be the answer. I'll kick off a test tap later today.
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Re: Drilling holes in stocks for the centres

Postby nic » Mon May 28, 2012 11:09 am

I find in wood you can make whatever thread you have into a tap. All you need to do is put three short cuts with a file or angle grinder, across the first few threads. If you have a look at a tap you can see what angle you need to use to imitate the cutting angles. Will clog on the long holes you are talking about, though so might need frequent clearing. As Bob said grease really helps.
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Re: Drilling holes in stocks for the centres

Postby Bob_Fleet » Mon May 28, 2012 11:49 am

Went well yesterday
10mm holes for 12mm rod.
Fit the poppet and wedge tight onto one end of the bed.
Mark the height (make sure the handle clears the bed as it turns)
You can line up on the centre of the slot
Get two folk with mark one eyeballs to help keep you in line
One at the side to keep you horizontal and one in line with the bed.
If you use an electric drill there is less movement and you are more likely to end up straight.
It's the only bit we use power (battery) for.
Once the long spindle is in then use it as the others say to mark the fixed one.
Sorry but forgot to take pics.

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Re: Drilling holes in stocks for the centres

Postby emjay » Mon May 28, 2012 9:29 pm

Nic. If you make those file cuts with a slight left hand twist, then the swarf will fall out in front of the "tap".
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Re: Drilling holes in stocks for the centres

Postby nic » Mon May 28, 2012 9:38 pm

I never thought of that,thanks. I'll give it a go next time I make one. Actually, Its only a two minute job so I'll give it a go tomorrow- wood 'swarf' tends to jam at any opportunity and I'm intruiged to see if it will work.
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Re: Drilling holes in stocks for the centres

Postby jrccaim » Wed May 30, 2012 5:23 am

I have a rather long post somewhere in this forum on the topic, so I will be as brief as I can (I can hear the sighs of relief from everyone :))

Look, the holes (a) have to be square to the poppets and (b) have to line up. What I do is drill the headstock first and put in the center. Then I shove it over and use it as a center-punch for the tail. Then drill tail. You must have a really good square. When I drill, I tape a line level to the auger bit. I lay down the square to give me square and the level to give me the other dimension.

Now as to self-tapping. You can probably get away with this. But maybe not. Depends on size of tail center and your assortment of bits. There is a formula for this purpose. It is drill size = outside diameter - pitch. (This gives you 65% coverage. Good enough for all practical purposes). So, for example, you have an M8/1 bolt (8mm outside diameter, 1mm pitch). Most 8mm bolts have 1mm pitch. So drill 7mm. Formula works in any units, but I refuse to deal with insane fractional inches. If you want inches go look it up on the internet, and be prepared to deal with Morse number drills. Google on "tap size," for instance.

And further, the oh no! situation. So you do your best, and in doubt drill undersize. If the thing is too tight, go get a taper tap and run it through. Taps are not expensive. If it is too loose, all is not lost. Get a smallish piece of plastic. A piece of garbage bag will do. Roll it up tight around the bolt and screw it in. It will provide enough friction to run your tailstock properly. These remedies are based on personal experience, not hearsay. One of my lathes was too tight, and another too loose. I did as I advise.

I recommend a set of basic taps for anyone who builds stuff, lathes in particular. I have a set that goes M4-M12 and 4-40 to 1/2"-20 for inch fanatics. Cost $30 and I have never regretted it. I recommend taper taps. I can hear five generations of machinists howl :) but taper taps are much easier on beginners than bottoming or finishing taps. If you have never tapped a hole before, there is a cardinal rule. Start the b---y thing dead square fore, aft, port and starboard. Use any means at your disposal to do so. A small square, or even two, is a great help. Two dimensions, you see. If you start the tap right you will have no problems. If you don't there is no fix for it.
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Re: Drilling holes in stocks for the centres

Postby gavin » Wed May 30, 2012 7:23 am

jrccaim wrote: I have a set that goes M4-M12 and 4-40 to 1/2"-20 for inch fanatics..

What does "4 -40" mean?
What does the" -20" mean here: 1/2"-20
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Re: Drilling holes in stocks for the centres

Postby Darrell » Thu May 31, 2012 3:16 am

Hi Gavin,

Those are tap sizes.
1/4-20 is a 1/4 inch diameter, 20 threads per inch.
Just look up thread sizes on Google, like this http://www.engineersedge.com/screw_threads_chart.htm

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Re: Drilling holes in stocks for the centres

Postby jrccaim » Sat Jun 02, 2012 4:37 am

Amazing. I just put a post in this forum on the size of tapping holes. No doubt some other thread (no pun intended), or maybe it didn't take! Well, as Walt Whitman (no less) said, "do I repeat myself? Well, then I repeat myself." Here's the tapping formula again: tap hole = outside diameter - pitch of thread. Example: M10 x 1 bolt. (10mm outside diameter, 1 mm pitch; most metric threads are 1mm except very fine threads). So drill a 9mm hole. Works in any units, but metric obviously easier to figure. This is metal, and 65% thread coverage; adequate for all practical purposes. Since we are dealing with wood there is some slop. You might get away with an 8mm hole in wood for an M10 bolt. You will get better than 65% coverage. It will also be much harder to turn at first. So oil it well and turn back & forth it a lot, and you may get it to bend to your will. Whatever you do, start the bolt square to the hole. Myself, I prefer taper taps, but that's just me. Much easier to start a taper tap than raw bolts.(But then, I have taps M4-M12 sizes :) plus gringo from 4-40 to 3/8-20 and I paid $30 for them. Corresponding dies included.)
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Re: Drilling holes in stocks for the centres

Postby voodooalpaca » Wed Jun 06, 2012 11:38 am

For my 12mm thread I did the following

Drilled a 10mm hole.. Used longest drill bit I had and measured lots, to ensure it was accurate.
Put both poppets on the bed and poked a centre mark from the drilled one to the un-drilled one to ensure accurate alignment.

Tapped about half way through (that was as far as I could get with my little taper tap set) Metal cutting tap of course. a squirt of WD40 to lube, massive difference!

Screwed in the thread, all the way (i.e. cut new thread in the final half), more WD40 lube.

Removed the thread, and tapped from the other side with the metal cutting tap. This made the thread easier to use, yet still tight.

Thread was from Screwfix, A2 Stainless (which was in "stock" in my workshop), ground to a 60deg point on a metal lathe, little cranked handle (bent bit of metal) welded onto one thread

Lathe bed and frame made now, just need to make the treadle and bungee.

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Re: Drilling holes in stocks for the centres

Postby jrccaim » Thu Jun 07, 2012 3:56 am

voodooalpaca wrote:For my 12mm thread I did the following..


Bravo voodoo alpaca. (Nice wooly Avatar there BTW) . 1mm off my tap equation. Wood, though, doesen't make too much diff. Got some slop in wood. If you find it too tight work it back and forth a while. Oil liberally. Cheap veg oil fine. You're down to the last stages now.
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Re: Drilling holes in stocks for the centres

Postby tmb24wh » Tue Jun 12, 2012 9:04 pm

I drilled 10mm for 12mm centres which worked fine except during the cold damp months when the poppets swelled and the adjustable centre became almost too tight to wind in & out - as has been said already - lube it up, use beef dripping, lard, shredded candle wax... or grease I guess. I prefer dripping though :-)
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Re: Drilling holes in stocks for the centres

Postby jrccaim » Fri Jun 15, 2012 4:30 am

gavin wrote:
jrccaim wrote: I have a set that goes M4-M12 and 4-40 to 1/2"-20 for inch fanatics..

What does "4 -40" mean?
What does the" -20" mean here: 1/2"-20


As Darrel said. I have to deal with these things, living in the last unmetricated country in the world. But we inherited them from Britain! Common screw diameters are numbered. They go 4-6-8-10. You can get the exact diameters from Darrel's cite. After that they go in fractions of an inch. Common diameters are 1/4, 3/8, and 1/2. Pitch is expressed in TPI or turns per inch so a 1/4-20 is .25" diameter and 20 turns per inch, or 1/20 = .05 inch pitch. So the drill size is .25 - .05 or .20 " and I refuse to convert that to fractions :). Look it up. And mind, when you look it up, the numbers are for metal.

I recently have drilled a whole lot of holes in wood, for tapping. It all depends on the wood, but in summary you might want to drill somewhat undersize. How much? Wood dependent. Again, M8x1. Tap equation says 7mm. I'd now recommend 6.5mm. Softer the wood the smaller the hole you can get away with. Be sure to oil the tap. Any old oil will do. If you are self-tapping you might want to stick to the tap equation. Also oil the bolt itself. Any old oil, including veg oil, will do the job.
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