BCA Jig Borer MK3

[William SParticipant @williams]

Help with the belt tensioning spring required.

[William SParticipant @williams]

Hello all

The beginning of July saw us acquiring a used, if a little abused MK3 BCA Jig Borer

All ready being put to use!

It came with; the original cabinet and light, currently in the house as a TV stand as we don't have room for it in the shed! a full set of imperial collets and some duplicates, 2 drill chucks, a large and a small boring head, A Sigma Jones table, and other bits and pieces as well.

When I say used/abused from what I can gather it was used by a company specialising in aluminium cnc work so the BCA mostly being used for its intended purpose as a drilling machine as opposed to a mill, The most wear being in the up and down feed, A good strip down, clean and adjustment, has meant that it is all tight with no real issues.

Now the main part that we require is the belt tensioning spring, as ours is missing, We have been in contact with tenga engineering as there website states there were the original manufactures of the MK3s, we needed another part which they supplied but they did not have any info on said spring, so now we ask here.

If a BCA owner would be able to give us the relevant information on the spring it would be very much appreciated, E.G.. O.D, I.D, overall length, number of coils and wire gauge it would be very helpful.

Thanks in advance

William

[AStroudParticipant @astroud]

Hi William

I have a BCA Mk 111 and have just removed the spring , these are the measurements

L = 2.75 ins

OD = 1.03 ins

wire dia = 0.103 ins

Pic:

 

Hope this helps, Andrew

Edited By Andrew Stroud on 21/10/2018 12:34:54

[Michael GilliganParticipant @michaelgilligan61133]

Interesting … Mine doesn't have a spring.

MichaelG.

.

Sorry, I can't get at the literature today, but

I don't think I've ever seen one [until this thread] with a spring.  

Edited By Michael Gilligan on 21/10/2018 14:08:58

http://www.lathes.co.uk/bca/page5.html

Edited By Michael Gilligan on 21/10/2018 14:11:41

[not done it yetParticipant @notdoneityet]

Can one ask: What does the spring do?

The only thing it appears to be able to do is maintain a modicum of tension on the drive while the holding stud is loosened. Tension would be proportional to the compression of the spring, so rather a variable force. Or does it do something when apparently fixed in position?

I know nowt about the machine, but to me it appears that the spring is doing nothing to enhance the use of the machine.

[AStroudParticipant @astroud]

The spring keeps the belt at the correct tension, there is a clear instruction in the instruction book about adjusting the tension arm to the correct fixed length so the spring is compressed to keep the belt at the correct tension.

Andrew

[David TParticipant @davidt96864]

Posted by not done it yet on 21/10/2018 14:36:11:

Can one ask: What does the spring do?

The only thing it appears to be able to do is maintain a modicum of tension on the drive while the holding stud is loosened. Tension would be proportional to the compression of the spring, so rather a variable force. Or does it do something when apparently fixed in position?

It just applies tension, and the housing is only adjustable to account for different pulley diameters. BCA's only literature states that the correct tension is achieved when around 1/2" of the sliding shaft is exposed (naturally that assumes that the original spring is in use).

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Stroud on 21/10/2018 14:41:23:

The spring keeps the belt at the correct tension, there is a clear instruction in the instruction book about adjusting the tension arm to the correct fixed length so the spring is compressed to keep the belt at the correct tension.

Andrew

.

Wow … Do you actually have an instruction book for it, Andrew ?

[ green with envy ] MichaelG.

[AStroudParticipant @astroud]

Yes I do, but it is a reprint purchased from the lathes.co.uk website, quite pricey and a bit light in information but if you are a BCA enthusiast a must have I think.

Andrew

[Rob Jacobs 1Participant @robjacobs1]

Thread bump!

(Hello!)

Would anybody here be able to help out with some of the basics of this machine (BCA Jig Borer) please, such as how to remove the spindle slide, or how to enable the bevel function?

Please forgive the fact that I am brand new to this type of machine and it’s operations so I am very much still discovering the correct terminology. The problem is the machine I have needs some TLC and a good clean-up, but I can’t move it at its current weight, so removing sections to clean individually seems the way forward. The knee and table were easily removed, but as for the vertical slide … it appears to be bolted on either side, though the nuts are seized and I thought it best to query before getting myself into a situation. And if indeed these are the fixing bolts then I can’t see how it’s possible to swivel for a bevel.

A bit of a vague post I know, but if anyone has owned this machine or is at least familiar with it, help would be greatly appreciated.

Thanks, Rob

[William SParticipant @williams]

Good evening Rob

To pivot: The most important thing is to remove the Locating pin behind the slide on the main casting, it should be a tight fit, then slacken the 2 nuts either side, being mindful it will maybe want to fall to one side;

The nuts attach to basically T bolts that are in a circular T slot on the back of the slide casting;

Obviously to remove the whole assembly its a case of totally removing the 2 nuts and just pull it of the Centre spigot.

You say the nuts may be seized, in which case soak in penetrating oil. Just a quick point, I have done it myself! Is the spanner wedging up on the main casting in the cavity the nuts occupy? thus preventing it from turning

Last resort would be to cut them off as to remake the T bolts is a tad difficult as they must fit the circular slot. I think the middle picture above demonstrates this.

Good luck with the dismantling/moving of your machine, when we moved my 2 BCAs we just wound the table off and then did our backs in!

It would be nice to see some pictures of it

I hope that helps

William

(I do apologise for the orientation of the pictures they seem to be a bit drunk!, I can not seem work out the knack to upload pictures from my phone without them falling over)

Moderator edit: pictures fixed – not your fault William, it can happen to anyone!

Edited By SillyOldDuffer on 06/05/2021 18:37:54

[Rob Jacobs 1Participant @robjacobs1]

William thank you so much, that was exactly all the information I needed!

Nuts removed both sides and after some persuasion the bevel assembly freed up and gave way to movement – awesome! However the spindle assembly really doesn't want to pull off the front so I may investigate undoing the 4 allen bolts visible when at 90* to remove the entire top section.

One other query I have, would you be able to tell me the function of this lever please?

https://www.dropbox.com/s/fgvgovhcoasm01j/IMG_3846.jpg?dl=0

Side note: I am having difficulty uploading images, I hope the above link works? If it does you can probably see the rust which has taken over this machine and needs to be cleaned up!

Thanks again, Rob

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Rob Jacobs 1 on 06/05/2021 22:35:59:

[…]

One other query I have, would you be able to tell me the function of this lever please?

https://www.dropbox.com/s/fgvgovhcoasm01j/IMG_3846.jpg?dl=0

 

[…]

.

That lever isn’t usually left in place there … it’s a tommy-bar for the ‘capstan’ screw

[ No harm if it’s secure, I suppose …  it presumably goes through and has another  tie-wrap ]

… it locks the Z-axis

MichaelG.

.

P.S. __ Here’s ‘War and Peace’ on posting photos:

https://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

 

Edited By Michael Gilligan on 06/05/2021 23:04:09

[Dan ShoulerParticipant @danshouler67839]

Hello all,

Hoping someone on here could point me in the right direction. I have one of these machines, pretty much exactly as pictured, but sadly we were broken into and a part of this which I'd taken off and put on the neighbouring lathe table was stolen along with said lathe.

The part in question is pictured in William's 3rd picture from 6th May – that plate with the arm for the belt tensioner. Does anyone know where a replacement could be sourced, or failing that does anyone know where I could find a home for this sadly non functional machine? I'm loathe to throw away such a good bit of kit, but I'm similarly sad to watch it rust in the corner!

Many thanks,

[Michael GilliganParticipant @michaelgilligan61133]

Short of hitting lucky on ebay, or, homeworkshop, or this site … I think you would best contact Tenga : **LINK**

Home

They were effectively successors to ‘Bloctube Controls Aylesbury’ in manufacturing the machine.

MichaelG.

[Dan ShoulerParticipant @danshouler67839]

Thanks Michael.

Tenga replied quickly but sadly were unable to help as my machine it turns out is older, they estimate about 65 years. Tried a couple of other places but no joy so I'll put it up for spares and repairs on homework shop. Shame given it was a lovely piece of kit but hopefully someone else will find just the bit they need from mine.

Thanks,

[AJAXParticipant @ajax]

Posted by Dan Shouler on 02/08/2021 16:17:28:

Hello all,

Hoping someone on here could point me in the right direction. I have one of these machines, pretty much exactly as pictured, but sadly we were broken into and a part of this which I'd taken off and put on the neighbouring lathe table was stolen along with said lathe.

The part in question is pictured in William's 3rd picture from 6th May – that plate with the arm for the belt tensioner. Does anyone know where a replacement could be sourced, or failing that does anyone know where I could find a home for this sadly non functional machine? I'm loathe to throw away such a good bit of kit, but I'm similarly sad to watch it rust in the corner!

Many thanks,

Great shame that you lost a vital part. Why not try to sell it on eBay or offer it here? There are lots of people (including myself) who enjoy a challenge at resurrecting an old machine.

[Chris Cartwright 2Participant @chriscartwright2]

Hello all,

I too have a somewhat battered BCA. I've got two problems with it that one of you experts may be able to help me with:

1) There is a LOT of vertical play in the spindle (like 5mm+). I get around this by using the locking lever every time I mill something, and always approaching a set point downwards (with gravity holding the spindle against the stop), but I'm sure it can't be right.

2) My rotary table recently jammed up (i.e. it wont rotate). Presumably something inside has got stuck, but I can't see how to get it apart.

Any tips gratefully received.

Chris

Devon

[William SParticipant @williams]

Possibly not going to be seen, but I just found your post Chris Cartwright, I may do a pm and see if that gets through also.

Regards your query's, the down feed, (I think that's what you are talking about) my first thought is the leadscrew is not set up correctly, there should be 2 thrust bearings either side of the bearing block just below the ball handle, this is adjusted (on a mk3 mark 2s are the same I belive though) by undoing the top lock nut and nipping the cone nut up inside the ball handle, I use a pair of circlip pliers in the 2 holes. (I can supply pictures if required, even better if you could supply pictures)

Another thing that I can think of is the slide may be set up a bit tight, on mine any backlash is really taken care of by gravity, if the symptoms of 5mm present themself when winding the slide back up the, I would say it is too tight, (gravity should be pulling the slide against one side of the nut.)

The manual does say to lock the unused slides when milling so with you locking it there's nothing wrong with that!

Regards the rotary table, sorry if you have already checked this but are the locking bolts loose, is the table able to free spin with the worm disengaged?

The slide has to be wound off to remove the rotary table ,the rod holder block may have to be removed first to allow the rotary table lock bolt too be unobstructed. Turned upside down to reveal 3 socket head bolts that secure the taper spigot to the bottom of the table (remember to mark the orientation of this in relation to the table.)

I hope you find this and it makes sense. Any other help please ask, if you can supply pictures that would be great.

William

[Mark RandParticipant @markrand96270]

The Mk2 machines didn't have thrust bearings on the feedscrews, but play was taken up in the same way was the mk3s, by tightening the nut that holds the handle on (and locking it with the lock nut).

For the spindle, the end play is adjusted with the nut and locknut on the spindle above the top bearing. The bearing clearancesare adjusted with the nuts above and blelow the bearings. Adjust the latter until there is a slight drag on the spindle (if they're loose you will get chatter). Adjust the end play until there isn't any.

On both versions, the rotary table is held with a slotted nut on it's mounting boss, which can be found by winding the Y slide off the machine and turning it all upside down (it's heavy with the table as well). There is a clamping screw in the face of the nut to unlock it. As William says, the most obvious causes are the locking bilts on either side of the underside of the table, or possibly some dirt in the wormwheel threads.

[Chris Cartwright 2Participant @chriscartwright2]

Thank you very much Mark and William!

I will head to the workshop tomorrow and investigate.

Best Regards, Chris.

[Chris Cartwright 2Participant @chriscartwright2]

Well I can't see anything to adjust the vertical slide other than the handle screw (grub screw with two diametrically opposite slots). Under the handle is only a cylindrical part with a keyway and key, which seems to rotate freely without grabbing anything.

I've taken it down to about 1mm play using the grub screw (i.e if you lift the slide assembly against gravity, it moves about 1mm). As William said, gravity holds the assembly against one side of the leadscrew, so when winding it up/down there is basically no backlash. However, when the milling bit contacts the workpiece, the backlash is taken up before milling commences, making it difficult to set depths accurately.

Re the rotary table: The locking nuts are free, and the table will only move about 1-2 degrees, with or without the worm engaged. Any thoughts on this before I start dismantling the thing?

Cheers, Chris.

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