Drill and tapping flywheels to take an M3 grub screw.

Some flywheels are easy to drill and tap for a M3 grub screw as the hub projects out a long way. But with some flywheels the hub lies well inside the vertical plane made by the outer rim of the flywheel. How do you drill and tap the hub on such a flywheel ? I am having problems getting the drill bits and taps in there as the drill chuck and tap wrench get in the way. The drill bits and taps are not long enough.

Edited By Brian John on 25/02/2016 06:15:01

YOu might be able to set the flywheel up on the drill press at an angle of about 30 degrees so the rim of the flywheel clears the drill chuck. Using a small drill chuck means a small angle required.

The problem then is trying to get the hole started on an angle surface without the drill bit flexing and wandering about the place. Use a good stout centre drill to get the hole started. Or even mill a small flat where the hole it so go by using a small slot drill or end mill, available cheap in small sizes on the net and can be gripped in the drill chuck.

Way to set the flywheel at an angle might be to grip it in the vice then put packing under one end of the vice.

Or you can machine a keyway in the shaft and one in the flywheel hub.

Long seies centre drill to start the hole and then long series drill bit. Tap can be stuck into a simple extension with loctite and then removed when done

Can be held like this

I tilt the fly wheel, and use a long series drill/ or an ordinary one held at the very end, with the shank of the drill, almost if not actually touching the rim. I,v seen me putting the tap in with a 4" Crescent spanner, no room for a tap wrench. Use a round ended grub screw. On my hot air engines where I swap fly wheels, pulleys quite often, I use brass grub screws so they don't mark the shaft, no good on an IC engine.

Ian S C

I have used ER11 collets in a Ø16mm shanked collet holder to hold small tools for accessing setups like this. It will not give enough clearance on very small flywheels or ones set at a small angle but is better than a full sized chuck for some jobs.

Martin

This is how I did it when I built my first engine.

I cut off a scrap of soft wood at 45 degrees in a mitre box, screwed the flywheel tightly to the wood off-cut which was then clamped to the drilling table of my lathe.

Bear in mind, that it is a small flywheel and a small Unimat lathe/mill/drill. Anything larger would probably have needed a far more secure method of holding the flywheel.

Clive

A couple of more bizarre ways one might do this.. using a highspeed dental handpiece and round bur but accepting this would be a handheld hole and need a self-tapper into the softer alloy.

The handpieces are available as cheap versions..just need to make soms mods or buy adapters to work off an ordinary compressor and fix up a coolant supply but fine dental burs really don't skip much on a round surface and then go up in size. Getting a tap in would be the problem but might be do-able if the rim is far enough from the hub.

Another option whicvh would have worked on the flywheel I made for my stirling .. the hub was a subunit pressed into the middle ('cos i didn';t have a thick enough steel plate for the hub width).. so make the hub centre and pre-drill/tap before pressing with a slot filed at the base of the spokes to match that hole...

I have ordered a longer 2.5mm drill bit (101mm) as my current drill bit is only 55mm. At 101mm long I would prefer to use 2.4mm as the tap drill but they do not have them at 2.4mm. I am already holding the flywheel in the vice and using timber under the vice to get a good angle. I punch a small mark on the hub to give the drill bit a starting point. All this works quite well but then the main problem is the M3 taps which are quite short. At the moment I am getting it done by just holding the end of the tap in the tap wrench by about 1mm but this will not work for some of the larger flywheels I have.

Jason : can you post a photo of your tap extension if you have one handy ? I have a few ideas in my head but I would like to see what you use.

Edited By Brian John on 26/02/2016 07:32:48

I did look for one yesterday but could not fine one with a tap.

For M3 take a piece of 5mm or 6mm roudd steel, face off the end in the lathe and then drill it so that the shank of the tap is a good fit in the hole and say 15mm deep. Clean the tap and loctite or superglue it into the hole and leave to set. You now have a long tap which will reach where you need.

Once the job is done heat the rod being careful not to overheat the business end of teh tap which will make the loctite joint fail and you can pull the tap out of the hole.

This is the same principal with a drill bit on the right

The 2.5mm drill will be idea, 2.4 is getting a bit tight for M3

Yes, but the longer it is, the more it wobbles at the tip hence probably producing a slightly larger hole than intended.

Thank you for the photos.

If drilling at an angle would it be a good idea to use a copper slug between the grub screw and the shaft so that removal of the flywheel might be facilitated at a later date?

I must get some photos of my latest flywheel, it uses a tapered collet to hold it on the shaft, no grub screw, this one is for a 8 mm shaft, but could go to at least 5 mm, if not smaller, I tend to make my crankshafts a little bigger than in some published designs. On very small flywheels it is possible to go straight in through the rim, that's what we did when we made a little steam engine at night class at the High School, we drilled tapping size to the bore, then drilled clearance size to within about 6 mm from the bore, think the clearance was 3.5 mm to clear the shank of the 3 mm tap.

With Kwil's method, the copper slug would conform to the shape of the shaft, and lock well with not too much force, and an ordinary grub screw can be used, or a bit saved from shortening screws can get a slot cut with a junior hacksaw.

Ian S C

I have spent the afternoon making this tool from 1/4'' round brass...well, I spent most of the afternoon thinking about it and much less time making it ! I drilled and tapped the main brass shaft to take two M2 X 2mm grub screws : this holds the square part of the tap. There is one grub screw on each side. I did think about going for four grub screws but decided to stick with two for now. I drilled and tapped the shaft right through at the other end to take an M3 X 20mm pan head screw. The head was cut off leaving just the M3 thread exposed on either side. The tommy bar was then made by drilling and tapping the ends of  two pieces of 1/4'' brass which were screwed onto the thread.

It actually works. I can get in closer to the hub of the flywheel with this tool and no Loctite required. The only problem I had was the hex tool to tighten the M2 grub screws. I  had four 0.9mm hex tools but only one fitted the grub screws and the others did not as they were too small. I thought 0.9mm AF was the correct hex tool for an M2 grub screw ?

A smaller shaft [less than 1/4''] would probably require Loctite as there would not be enough thread on the grub screw to adequately grip the end of the tap.

NOTE : I do not understand why a copper slug should be used under the grub screw ?

Edited By Brian John on 27/02/2016 06:38:02

Edited By Brian John on 27/02/2016 06:38:42

Grub screws are usually a lot harder than the axle/shaft they will bear on so as you tighten them they damage the shaft. This can make it hard to remove the flywheel and does not look good either.

You could put a flat on the shaft for the screw to seat on which is a good way to do it particularly if you don't need to adjust the position of teh part.

For things like eccentrics which can need adjusting a small piece of copper of soft aluminium poped into the threaded hole first will get squashed down onto the shafft by the screw but being softer than the shaft won't leave a mark.

Small low quality allen keys can round over quite quickly and start slipping in the screwhead, try grinding a little of the end away to remove any rounded corners.

I use brass screws on most of my pulleys and flywheels on the hot air engines.

Ian S C