Lathe headstock bearing access

[Mike HurleyParticipant @mikehurley60381]

I need access to a bearing in the headstock of my old BV-20 lathe. The ends of all he gear trains are covered by a ‘plug’ which I need to remove. Each has a small (5mm) tapped hole in the centre.

I assumed this thread woud allow me to either a) fit a screw and use it to ‘jack’ the plug off or (b fit a lashed-up extractor to pull it off. Neither method has been successful. The threadsize is so small I don’t dare put to much force on it as it’s so light it may just shear off (have tried until I literally couldn’t turn the allen key any more.)

So, anybody seen / done this before? It seems overkill to start drilling holes / applying excessive force at this stage. Any suggestions appreciated

Mike

[mgnbukParticipant @mgnbuk]

That style of plug was usually removed with a slide hammer when I used to work with such things. All the fitters had some form of slide hammer in their toolboxes – usually “home made”  and with interchangeable threaded ends to suit different applications.

Nigel B.

[Mike HurleyParticipant @mikehurley60381]

Many thanks Nigel, hadn’t thought of that one. I’ll lash something up when I have chance and give it a go.

Regards Mike

[Dave HalfordParticipant @davehalford22513]

The same plugs are used on the 2a/b Centec’s, which probably explains why most of them have thread damage to the bolt hole if they had slide hammers used on them.

I used a 2 ” long slab of 6mm steel drilled for the plug hole and another 2 holes tapped m8 which bear either side of the cap. Fully tighten the m5 till it bottoms and then tighten m8 bolts alternately to jack the plug out.

You may find the bearings need to be tapped out with a drift as well unless there are C clips.

 

[old martParticipant @oldmart]

If you end up stripping the M5 holes, you may not have any choice but to drill right through the plugs with a larger drill to tap them out to 8mm which would be much stronger. Drilling right through will be ok as the shaft has to be removed anyway and any swarf can be cleaned before reassembly. Start with a decent 5mm SHCS and remove any end chamfer to ensure the threads have the best chance of holding. If you have to resort to drilling right through, the hole can have a short countersunk screw in it as a plug.

[Mike HurleyParticipant @mikehurley60381]

Thanks Dave & old mart. The heavy duty puller worked a treat! Found a bar with a couple of holes near the end that I was able to tap M8. It was surprising how much force I had to use and still the M5 screw didn’t strip! Pulled the plug out no problem.

Anyway, thanks again for the most useful input. regards, Mike

[HuubParticipant @huub]

I think the correct way to remove the cap is to screw a bolt in the hole and once the tip of the bolt gets to the shaft, the bolt will pull the cap out of the socket.

[Mike HurleyParticipant @mikehurley60381]

First thing I tried Huub – as I noted in my original post

‘I assumed this thread would allow me to either a) fit a screw and use it to ‘jack’ the plug off or’  etc

I literally couldn’t put any more force without shearing off the allen key.

regards, Mike

[duncan webster 1Participant @duncanwebster1]

When turning a bolt in a threaded hole, a lot of the effort goes into friction under the head and between the male and female threads. This means that the bolt shank has to resist both tension and torsion at the same time. Doing it with the goal post arrangement means the M5 bolt only has to resist the tension.

[HopperParticipant @hopper]

It helps too if you put some tension on the outer screws then whack the centre screw with a hammer a few times. A lot of times the impact shock of the hammer blows will work better than the steady force of the screws alone.

[Clive FosterParticipant @clivefoster55965]

When using a puller like Mikes’ it’s best to put a spacer between the parts being pulled and the bar so the centre screw or bolt can be done up tight. Effectively becomes a single solid unit vastly reducing the chance of thread stripping.

Way back young and hairy Clive stripped the thread on the centre bolt doing a similar job, fortunately not the extractor thread on the part being removed. Was advised to make things solid with a spacer and it all came out quite easily. As I recall it with less torque on the pulling bolts too. I presume with it all locked up solid the mechanical efficiency at actually pulling is much greater. Or something.

Probably unwise to use a high tensile bolt in the middle. Nice fitting ordinary bolt, something better than the rattle around big box store cheap ones, seems wise. If everything does go whaooie shape a HT bolt could well strip the thread in the part being removed. Which makes the problem ten times worse. An ordinary bolt stripping leaving the other thread intact is much less of an issue.

If need be and you have the facilities make your one with a top limit size thread for best grip. Something I’ve done in the past when I really didn’t like the potential fall out if things didn’t work.

Clive

[mgnbukParticipant @mgnbuk]

It helps too if you put some tension on the outer screws then whack the centre screw with a hammer a few times. A lot of times the impact shock of the hammer blows will work better than the steady force of the screws alone.

Hence suggesting the use of a slide hammer, as my former collegues used by default. The home made pullers used socket cap screws to engage the threads, with the screws tightened up into blind threaded caps or with a locknut to secure through threaded caps so that the threads wer not “loose” & subject to shcok loads – effectively doing as Clive suggests. I don’t recall stripped threads being an issue.

Nigel B.

[Dave HalfordParticipant @davehalford22513]

Yet a good number of Centec 2A & 2B photos which aren’t adverts show craters around the 2 cap holes from numpties who can’t tighten a screw far enough.

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