Meek bigbore dog clutch

[Bjorn_B]

Made a mistake  (often do) with the diameter of the bore for the indexing sleeve (should be 22mm, was 20)

So I had to pick up centre and adjust the diameter with a boring head

20160423_090757 by Bjorn Bursell, on Flickr

Indexing sleeve is a ordinary lathe job up to this point, a few holes has to be made across it. One of them is quite large so a drill is out of the question, as the boring head was set up in the mill I did it this way

20160423_095529 by Bjorn Bursell, on Flickr

20160423_101038 by Bjorn Bursell, on Flickr

[Bjorn_B]

Got a bit more time of today so I made the indexing unit. Made 90 degree toolbit on the Quorn and set to work, quite a broad cut in the middle (1,5mm deep and 3mm wide) so low revs and a lot of oil.
20160423_163758 by Bjorn Bursell, on Flickr 

After setting up in the dividing head and drilling/milling slots and holes the result is this after hardening (silver steel for this part)
20160423_173116 by Bjorn Bursell, on Flickr

Coming along nicely, family photo so far
20160423_175154 by Bjorn Bursell, on Flickr

I guess the selector fork comes next, oh, I also found a bag of steel bearing balls (1/8"). Must have bought it when I renovated an old bicycle, pedal bearings? Will be good for the indexing detent.

[Bjorn_B]

There seems to be a need to do "some" modifications on this casting.. hm..
20160424_101321 by Bjorn Bursell, on Flickr

This might be an issue because I have a big-bore myford, dunno how much of a clearance issue there is on ordinary S7. Anyways, better get on with the job in hand, it has already been hacked for a drop-bolt on the bottom part. Up on the mill table it goes..

20160424_104235 by Bjorn Bursell, on Flickr

Bit brutish maybe, but clearance for trip arm is needed (check) and there is also clearance enough (I think) for the disengage modification of Ken W. I will have to machine a bit of the gearbox top lid and a bit more of this casting in the lever arm boss area for this.

20160424_113223 by Bjorn Bursell, on Flickr

[Graham Meek]

Nice photographs Bjorn,

I did not realise that so much material would have to be removed from the inner guard.  The original S7 versions that I made sat just above the inner cover and only the slot for the trip rod actuating lever was required. Perhaps Myford altered these covers on the Big Bore to stop the ingress of swarf that sometimes happened with the S7, alas we will never know.

My best regards
Gray,

[Stuart]

can i interject here

mine only required a small slot to allow the operating shaft to ge to the saddle

it was only the size of the blue mark on the right of the second picture

it looks to me that Bjorns one is sitting to far back as mine does not foul the top of the casting at all if it did i would have told you about it

as you know the distances below the banjo pivot point is the same on all the S7 variants its only the distance above that point that is altered else the standard gearing would not fit in the fixed change wheel banjo


hope you are feeling better got a few questions for you but held off when i heard you had a new medical problem

Stuart

[pgp001]

Here is a photo of my standard S7 for comparison.
Again, just the slot for the trip lever was needed.

Does the "Big Bore" have a larger gear on the main spindle, if so this will push the whole clutch unit further down.



Phil

[Stuart]

Thats all I had to do to my conny

and yes it does

Its the same size as the dog clutch gear see att. 38 T 20 dp

the input gears are 20 t 20 dp

on the BB very the leaver shaft is lower due to the lager gears above the banjo pivot but below its the same

i note in Bjorns first post he mentions altering the body due to some clearance
Stuart

[Graham Meek]

Hi Phil, Stuart,

Thanks for the additional information. I was beginning to think I had got it all wrong, as I did not have a photograph of the finished BB item actually installed.

My best regards
Gray,

[Stuart]

More info

all this fouling that is present on Bjorns build had the brain cell working and seeing Phil's pic made me go and have a look see

a quick measurement for Phil spindle centre to banjo centre is Approx 85 mm give or take do not machine anything to that dim

I cannot get a camera in to take pics it has only enough room to open the cover, so to close to get in

but I can see that my fixed cover is different to Bjorn's the rear is the same,  but its cut away from new in a big scoop where Bjorn has cut it out thats why i did not need to alter mine in that area hence no heads up to Gray

i have 3 mm clearance at the rear of the body to head casting

now a bit of history on my lathe when i placed the order it took them a year to get it made ( now this was a short time before the sold out ) the reason they gave to me was that they where redesigning the headstock casting that supports the counter shaft , I just wonder if they also played around with the fixed guard as well , i have seen another with what looks like the S7 fixed guard ( note I only live 5 miles from the nottingham factory ) but i do not think that was the only change they made in the spindle area .

as I have said in the past they are not all equal measurements do vary and parts were changed  I think that were using up the bits that they had at the time and maybe mine has a prototype cover we will never know

Stuart

[Bjorn_B]

this is all very interesting, thanks for all your combined input!

Perhaps some of the difference in my back cover compared to stuart is explained that my bigbore is quite early (one of the odd 67t bullgear examples) can't remember the serial number, but it was made in 2002. It was made as a metric machine with induction hardened bedways and gearbox. I have since upgraded the bullgear/pulley assembly..

Below is a photo of the headstock/back cover alignment, the back cover sits a fair bit proud of the bed/headstock (sorry, lots of swarf..)
20160424_101326 by Bjorn Bursell, on Flickr

[Bjorn_B]

On a sidenote, I'm thinking of modifying the body slightly to make for more room to tilt the body forwards (disengagement) as the operating lever will hit the gearbox lid otherwise. It is now very close so I doubt that enough clearance can be machined away without having a permanent inspection hole...

It is perhaps possible to put the operating shaft about 6mm higher, closer to the spindle. Another option (that I have not looked in to yet) is to use a 29t gear on the first input shaft (needs to be moved somewhat aft for that). and let the whole thing tilt a little bit backwards when engaged. I need to measure how much "tilt" in degrees one "notch" of the tumbler reverse index gives and go from there before deciding anything..

Ah well, it is a perfect job for the 3D printer to make a mock-up of this whenever it arrives..

[Graham Meek]

I have just been taking a look at some of the photographs used in the original article and some I think Stuart supplied back in 2014 when we worked out the BB design. If you look at the original S7 the inner cover is tight up against the end of the bed, but in the BB photograph there appears to be a gap similar to that on Bjorn's machine. Zooming in there is a loss of clarity but there is definitely a gap.

As far as I can remember the position of the QC box determines where everything sits, so the tapped holes holding the box have either been moved, or they were in the wrong position in the QC box. Without a detailed measurement of the components against the works drawings this conundrum is going to be open to interpretation.

My best regards
Gray,

[Stuart]

Gray
Don't think that is my BB as the wall is white and I have a insert in the door to stop swarf getting in and to cover the mess in the end and I use a knurled draw bar

But my cover is much closer to the head stock where that one shows the cover the same as Bjorn's mine dips away

Stuart

[Bjorn_B]

This early bigbore has a back cover just like mine, http://www.lathes.co.uk/Myfordsuper7bigbore/img19.jpg (mine is SK111768, that one is very close at #111775)

Seems that somewhere along the line, they did a redesign of this.

[Bjorn_B]

After some measuring, I found that there is about 9,2 degrees of rotation between two "notches" on the tumbler reverse plunger. I do not think it is possible to rotate the whole thing forwards by that amount so a compromise is on my mind, how about forwards tilt of 4,6 degrees in the free position and a backwards tilt of 4,6 degrees engaged. I guess a small modification to the trip arm is in order, but otherwise I can not really see any drawbacks.. With a small redesign that raises the operating shaft in the body there is ample room for this

20160425_185829 by Bjorn Bursell, on Flickr

Started scetching out ideas for new positions of input gear shafts on the body..