How do I do this?

[vcutajar]

Good day all

I am at the moment building the Westbury's Kiwi Mk2 engine and have a build log running in another part of this forum. I have finished the crank and now working on the bronze counterweights which will be bolted to the crank webs.

The holes in the crank webs (see photo) will be drilled 3mm clearance and possibly counterbored 5.5mm or 6mm. I do not have a problem drilling the 3mm holes by using a long drill but the counterbore I can't figure out how to do it. As you can see in the photo, the crank will be held in the vise upright for drilling and counterboring, but the shaft is more than 2" long. I have a 3mm counterbore which might be long enough for the job but that would increase the 3mm clearance hole to 3.2mm which I would like to avoid for this job. I thought about using a long 6mm endmill that I have which just might make it but would need to be held by the tip of the shank only so not very safe. Another option I am thinking about is using a drill and grinding the tip flat, but I have never done this and do not know what would be the end result.

So the question is, is there a simpler way of doing the counterbore that I am missing? Thanks for your patience in reading this long post.

Vince

 

[90LX_Notch]

Vince-

I would make some type of an extension holder for either the c'bore or the endmill. The easiest would be to to make one with a set screw and grind a "Weldon" flat on the tool you want to use.

-Bob

 

[steamer]

You could make your own co-bore with a 3 mm pilot and long enough to reach?

Use 0-1 drill rod.....or "Silver Steel" on the other side of the pond....harden and temper to straw yellow.....the cutting end is the end that needs to be straw yellow.

Dave

 

[lensman57]

Hi,
See the link attached for making your own or you could actually buy extra long series 6mm end mill but they are not cheap and for a one off job it is not worth it.

http://www.deansphotographica.com/machining/projects/mill/cbore/cbore.html

Dean is also a participant of these forums.

Regards,

A.G

 

[Mainer]

I think I did it with a 7/32" end mill (I gather that you've converted that to 6mm). As somebody already suggested, it's not difficult to make an extension. If things are really tight, you can make the extension just over the shank diameter of the end mill and use Loctite to hold the end mill in place. That way you don't to make the extension large enough to accept a setscrew. When you're done, chuck the assembly in the lathe and turn off the extension.

 

[MachineTom]

A 7/32 counterbore would be a 1/4 shank, In less time than it takes to type this, a 1/2 piece or steel rod, drill then ream or bore a .251 hole, then a hole and threaded for a set screw, #6-8, cut about 2 1/2" long an stick in DP, counter bore the holes.

I do not understand the point of a 3.2mm counter bore, I assume there are socket head bolts going into the #5 if the hole is called a 1/8" bore with a 7/32 counterbore that is .219. There is something missing in these numbers? ???

 

[Jasonb]

As Vince is from Malta I assume its being made in metric. 3.2mm is the standard pilot on a counterbore for M3 socket heads but I assume the OP wants to keep the clearance a tight 3.0mm to reduce the risk of the weights moving about.

I would make an extension and fit a FC-3 type cutter in the end, far more rigid than a long series cutter. You can use the same extension to take a center or spotting drill to start the hole if you don't have any long series center drills

J

 

[vcutajar]

Thanks guys for your suggestions.

It seems the general concensus is to go for an extension which as Jason pointed out could also be used for the centre drill. I think I will give that a try. If that does not work out then I will try and do my own counterbore as Dave and lensman57 suggested (loved that site you pointed to).

As Jason said, I am trying to keep the 3mm clearance hole to reduce the chances of the weights moving about, and for the same reason the reason why I would prefer to do the couterbore 5.5mm as opposed to 6mm.

If there are more ideas, bring them on.

Vince

 

[90LX_Notch]

Vince-

If you are worried the weights moving, pin them after final assembly/fitting.

-Bob

 

[AlanHaisley]

Vince,
:idea:
Consider making a c-bore head that you run upside-down: Run a shaft down through the holes, lock the head on with the cutting teeth facing UP, and raise the assembly to bore as needed. This would have the virtue of using the drilled holes as a ready-made pair of guides. I don't know if it would be easier or harder to do this way, but someday one of us will need to use a little trick like this and so I thought I would suggest it.
Alan

 

[MachineTom]

That tool is known as a Back Face, An arbor that fits the bore, and then a cutter that fits on with a 1/4 turn lock. Common in aircraft industry.

 

[Mosey]

Pictures??

 

[vcutajar]

OK guys, yesterday I made an extension from a piece of 10mm silver steel. The slot drill that I will be using has a threaded shank and I thought why not use it. I measured it and it seems to be 6mm X 1.25mm, but then I thought, does this metric thread actually exist? A quick search at Chronos ( a UK supplier) confirmed that it was not available. Searched the internet and found out it is an imperial thread with 20TPI.

So I scuppered the thread idea and drilled and reamed 6mm. Cleaned the bore and the slot drill with surgical spirit and used superglue to hold them together. Left it to cure 24 hours.

Today, I gave the extended 5.5mm slot drill a try on a piece of scrap mild steel. Drilled a 3mm through hole and counterbored with the slot drill. I am happy to say that it worked fine. I actually cheated a bit. Before counterboring, I drilled with a 5mm drill to a depth of 2mm so that I would give the slot drill less work to do.

Hopefully it will hold for the four holes I need to counterbore. I also made a similar extension for the centredrill.

After using the extended slot drill I would like to separate it from the extension. If I heat it up, would I be able to remove the slot drill? What do you think?

Vince

 

[steamer]

YES....but about 300 F and keep it away from your eyes and lungs as the glue can vaporize and go places where it shouldn't!

Outdoors would be best....

Dave

 

[vcutajar]

Dave

Thanks for the heads up.

 

[uli12us]

Although it's a rather old post, I grind for those problems a drill similiar to a wood Drill. I take a normal Drill with the needed Diametre of the large hole and grind it first that the chisel is very short. Sorry, I don't know the correct word for "ausspitzen" in english. After that I grind the Edges left and right to an angle of 90° until about 1/4 - 1/3 of the diametre is remaining. With these I drill in the centered workpiece to the correct deep. After that I drill in the centre hole with the small diametre.

Eventually, I make some pics from the part.

 

[bazmak]

Hi,if the c,bore is for a cap screw i usually use a standard drill and machine the underside of the capscrew at 118o.This gives a precission csk type of location so there is no play in the hole.You can use a long series drill to open up the 3.2 hole.
I have not used cbores as they are too expensive and specialized for most model engineers.Dont know if the end mill will work as it has no pilot
regards Barry

 

[goldstar31]

I'm in a bit of a hurry, plane to catch, wife disabled,me not very well at 84 but there are a few quick points about Westbury.
First, I don't think that he used a milling machine. In fact, I recall when he designed one- and I built one!
So you got back to the lathe- and think out what he did with the minimum of tools to this Kiwi crankshaft.
Obviously he used nothing more exotic than a D bit made from what we Brits call silver steel. Now this isn't magic or anything. It is what bagpipe makers have used to bore long narrow holes of up to 19 inches long. Now yonks ago, I did it but the trick is to steady the drill using the tail stock but you have to removed the tailstock poppet and put in a dummy piece of metal -or wood to act as a guide. Pipe making- not engine making.

Difficult? Pipe makers did this in shepherds cottages in the high hills using- their wife's steel knitting needles- by the light of a hurricane lamp.

If I recall, Westbury's mate- Neville Shute made engines- in the outback somewhere- without a mill. He made full size airships and wrote 'Trustee from the tool Room' etc.

Must fly!

 

[uli12us]

Modified drill and resulting holes.


Picture 004s.jpg

Picture 003s.jpg

Picture 005s.jpg

 

[bazmak]

As a sheetmetal worker we used to grind them and call them butterfly drills
ideal for drilling thin sheetmetal