Downham Mini Borer

[philf]

I'm hoping someone who has either a Downham or Elliott Mini Borer may be able to help.

A friend has a problem with a Downham Mini Borer. Last night I went to try to help him fix it but. between us, we failed miserably.

The quill is moved up and down from a graduated handwheel which turns a nut around a leadscrew. In trying to get maximum clearance between the tool in a boring head and the workpiece he has wound the quill up as far as it would go. Now it is firmly stuck.

Has anyone a copy of the manual for this machine (or for the Elliott Mini Borer which, I believe is mechanically identical) or does anyone know how to get at the revolving nut?

Tony at lathes.co.uk has the manual but at £37 my friend is reluctant to buy it.



The photo shows the auto-feed gearbox with its covers off trying to work out how to remove it. There appear to be only 2 visible screws and two dowels holding it to the quill housing. Is that all or are there any hidden screws? It doesn't want to come off.

Any help would be appreciated.

I've also put a request for help on HomeWorkshop.

Cheers.

Phil.

[DavidA]

I don't suppose that the problem is related to what appears to be a disconnected bolt at the top pf one of the right hand of two bars that retain the top plate. The one that seems to be at a strange angle ? Maybe jammed

Dave

[philf]

Hi Dave,

Thanks but - no - it's not that. I think that's just a scale and it can be slackened off and moved. The leadscrew (visible to the left of the quill) doesn't normally rotate. The nut (buried deep inside) revolves around the screw. If we slacken off the nut on the top of the screw we can only rotate the screw a degree or so. It's locked to the nut somehow.

I suspect the nut might be a two part anti-backlash affair and something's moved when he moved it perhaps further than he should.

He was part way through making his brother's Christmas present when it failed so he's been up to use my mill tonight to finish the job.

Cheers.

Phil.

[bertie_bassett]

cant help with a manual, but id say there must be a couple of screws on the other side of that gearbox? possibly need to dismantle the box to get at them though 

assume it jammed whilst running in autofeed?

[philf]

cant help with a manual, but id say there must be a couple of screws on the other side of that gearbox? possibly need to dismantle the box to get at them though 

assume it jammed whilst running in autofeed?

Hi bertie_bassett,

No - he was manually winding it up. The auto feed stop would have already have stopped it being driven that far.

The latest plan is to remove the nut from the top of the screw, lift the quill so the nut can be put on underneath the plate and then try to wind the screw down with a spanner.

I thought there may be one or two more screws but we can't get the l.h. cover off to see. I'm sure it will come off but I suspect there are some bearings pressed into it and pressed on the ends of shafts. It's odd there are two dowels adjacent to the two screws.

Hopefully the above plan will work but then he will have to concoct some method of stopping it happening again.

There is what may be a stop fastened to the bottom of the screw to stop the screw being wound out of the nut. I think this is probably wound up tight against the nut. Unfortunately it looks to held on with a csk socket head screw. These are terrible things and I won't use them. The hex size is usually smaller than the equivalent socket cap screw but the diameter is usually quite a bit larger. They lock very easily and more than once I've had to drill them out to shift them when the Allen key has rounded the hex without budging them.

Cheers.

Phil.

[bertie_bassett]

I'm surprised its gone that tight just by being wound by hand, though sometimes the tiniest thing can lock up a thread solid.

I assume you have tried shocking it? a dead blow hammer carefully applied to the screw may work?

for countersunk sockets Ill usually try an allen key just in case its loose, but then almost immediately pick up an impact driver, that usually does the trick