Tapping a thread where depth is restricted

[Tens]

Here's one for anyone mechanically minded.

A friend has an outboard where the steering is exceptionally stiff - common problem. It's quite old and not been used much. Our first port of call was to disconnect the steering cable to see if the problem is with the cable or the engine vertical steering tube thingy. ...... And it's the engine bit.

You really would expect there to be grease nipples so that the inside of the steering bearings/tube could be greased - but there aren't. To get it apart is a major disassembly job. It's obviously lubed for life..... or not.

Armed with a bit of clever thinking and Youtube, it seems the solution is to drill and tap 2 or 3 holes in the tube, fit grease nipples and work marine grease into it until it frees up.

I can see a problem, however, and that is, a tap has quite a bit of length of half hearted thread on it, to get it started, before it starts to cut the thread proper. I'm thinking that there will probably be a restricted gap inside the tube which will prevent the tap going deep enough to do a proper thread.

Does this make sense? Do I start the tap, and then grind a bit off the end, before doing a bit more, etc etc? Any suggestions? TIA.

[Doomanic]

What you have described is a home made bottom tap. That's what I'd do in your situation.

[Doomanic]

https://www.youtube.com/watch?v=2e7nc3Y5JzQ

[nigel hewitt]

And the cuttings go into the tube to which you have no access and that's going to free it up?
I hope I'm misunderstanding the situation...

[Nickpicks]

And the cuttings go into the tube to which you have no access and that's going to free it up?
I hope I'm misunderstanding the situation...

The swarf will mix with the grease and over time, will help to increase the clearance between the shaft and the bearing.

[Steve Clark]

Spiral flute bottoming tap.

[Tens]

Yay. Brilliant. Once you know what something like this is called, the rest is easy(ish).

The grease nipples are 6mm, so I'm hoping that the quantity of swarf will be negligible

Thanks for the help.

[Decosnapper]

The grease nipples are 6mm, so I'm hoping that the quantity of swarf will be negligible

Grease the tap as you use it to a) help the cutting process and b) give the swarf something to stick to.

When you wind the tap out at least some of the swarf will come with it.

[jamesp]

Spiral flute tap.
Calling it bottoming is a bit of a misnomer, as they are generally referred to as machine taps.
The flute causes the swarf to come "up" the hole.
There is still a "lead" (taper) on the start of the tap, of generally three thread pitches.

Nobody ever grinds those off, honestly!

As you said, start the thread, grind the tap; just make sure you grind it square, or you will have a world of poo open up.

What size do you need, I may have some part worn ones lying around I can post (M3,M4,M6 most likely) for you to play with.
Check your grease nipples, BSP are still very common for grease nipple threads.

[Tens]

Spiral flute tap.
Calling it bottoming is a bit of a misnomer, as they are generally referred to as machine taps.
The flute causes the swarf to come "up" the hole.
There is still a "lead" (taper) on the start of the tap, of generally three thread pitches.

Nobody ever grinds those off, honestly!

As you said, start the thread, grind the tap; just make sure you grind it square, or you will have a world of poo open up.

What size do you need, I may have some part worn ones lying around I can post (M3,M4,M6 most likely) for you to play with.
Check your grease nipples, BSP are still very common for grease nipple threads.

It's M6. Thanks for the offer! I don't want to put you to that trouble. I like buying stuff and they're inexpensive enough to get 2 or 3 to play with. Appreciate the offer though.

One thing, though. You say nobody ever grinds off the lead, but then you say start the thread and grind the tap. Can you elucidate?

[wibble32]

You say nobody ever grinds off the lead, but then you say start the thread and grind the tap. Can you elucidate?

I read it as irony or a wink.

Rgds

[Tens]

I read it as irony or a wink.

Rgds

Ah, missed that!

[jamesp]

It's M6. Thanks for the offer! I don't want to put you to that trouble. I like buying stuff and they're inexpensive enough to get 2 or 3 to play with. Appreciate the offer though.

One thing, though. You say nobody ever grinds off the lead, but then you say start the thread and grind the tap. Can you elucidate?

You will "need" the lead to start the thread square; then grind away.
Just make sure you grind the tap end square to axis.
I sometimes wonder if anyone actually uses tools as they come out of the box, I am always grinding away centre points, or shortening leads on taps: probably why I started using thread milling on small blind holes.

The ones where the designer wants 4mm of full thread, in a 4mm deep hole, with a 0.7mm pitch; and the lea on the tap is 1.5 mm; on a bottoming tap: That sort of everyday crap.

Given your location, I would be prepared to deliver.