Myford Super 7 with 'Big Bore Conversion'

I have been offered a Myford Super 7 with a 'big bore conversion', from a chap who modifies Super 7s to give a 32mm spindle bore. Also, instead of a morse taper, the new spindle has an ER40 collet taper.

I have several concerns which I invite your comments on:

1) The headstock has some modifications to accept the new spindle, including a change from the original plain bronze bearing to tapered roller bearings. The Amateur Lathe book suggests that roller/ball bearings generally lead to chatter at the tool. What do people think?

2) Do you think the boring of the spindle may leave it with walls that are too thin?

3) Are there any significant disadvantages to having a spindle without a morse taper?

4) Do you think that having a non-standard spindle leaves me open to spindle problems, since a replacement would not be able to be sourced and would need to be re-made, probably at a high cost?

Many thanks,

Mike

Ebay listing withdrawn for similar item. Seller cannot spell taper! Personally I would not buy it.

Is there a linkto this gentleman offers?

If rolling element spindle bearings gives chatter Schaublin ,Harrison etc was wrong.

Was author of Amateurs Lathe Book an amateur?

If the new spindle has 32mm hole, outside diameter cannot be less than 40mm.

Torsional and bending stiffnes is a power three thing.

If the original spindle has 16mm hole and 30mm outside we can compare:

4**3-3**3=64-27=36 and for theoriginal Myford 27-4.1=23 or the new is 36/23=56% stiffer.

Getting rid of Morse2 and having ER 40 sounds a very great advantage to me and I am going to try it on a pair of blue lathes from China.

Edited By Niels Abildgaard on 21/09/2018 19:17:48

Edited By Niels Abildgaard on 21/09/2018 19:18:16

Edited By Niels Abildgaard on 21/09/2018 19:24:51

He's been selling them for some time; from what I can see, the spindle must be a new replacement.

Why not contact the designer/modifier and ask him directly?

See one of the photos on this Completed Item Listing for a business card

I was at one time considering asking him how much for an exchange headstock, but never got round to it.

Obviously any spindle nose attachments you already own would no longer fit the modified end.

Bill.

The taper=chatter is a myth from the early days when taper rollers were in their infancy and many lathe users didn't have a clue how to adjust them. Probably every CNC manufacturing lathe on the planet uses taper rollers and how many turned items do you see with chatter marks?

British Timken wrote a three-page letter to Model Engineer debunking LBSC's complaints about taper rollers in the 1940s.

As for wall thickness, what is it? It would depend on the bearings used as well as the bore. Nils gives you a good idea how to judge.

Significant advantages to having an ER taper, how much MT tooling do you want to use in the headstock? You can always make up a dead centre to be held in a collet.

Spindle is unlikely to wear out and they are not difficult things for a decent machine shop (or anyone with a decent lathe) to make - you can finish turn the nose register and ER taper in situ.

My feeling is why not bring a 70-year old design up to date and give a good lathe a new lease of life?

Neil

That is what is known in the trade as a live centre...

Agree absolutely with everything else and might even have a go at upgrading the ML7 if I ever get all my other projects done .

Seems like a great idea, how can large bearings be inferior to a smaller plain bush ? ........ although most half decent industrial lathes seem to have headstock bearings which are super precision and made from a mixture of unicorn horn and dried pixie’s tears.....well judging by the cost, that must be the raw materials they are produced from.

So i suppose if the seller is using bearings from a far eastern destination, intended for use in trailer axle’s, or similar, then the quality of the cut might be questionable ?

Edited By Alan Waddington 2 on 21/09/2018 23:52:29

As for using taper tooling do what everyone with a large lathe does and use an adaptor to get down to MT3 or MT2, would simply need ER40 externally and can have the MT taper bored in situe.

Or change the few tools you may want to use to parallel shank and hold in an ER40 collet.

Don't see many Hardinge users complaining about having a 5C collet spindle socket rather than MT

Edited By JasonB on 22/09/2018 07:58:28

Ouch!

It's not the country of origin, its the quality of the bearings, you can get any level of quality you want for the far East and trailer bearings from Europe, if you want.

Neil

I bought a piece of (s)crap for 1100£ from UK.Testbar runout more than 0.1mm.

I have also bought a chineese 210 400 lathe for 600£ where runout error could not be detected with my swiss DTI

.

The general concept of this conversion sounds excellent, but I have a 'back of the mind' recollection that Myford [Beeston] opined that such a conversion was impractical, because the headstock casting was too small for it.

Things change [including bearing designs]: So It would be very interesting to know what bearings, and what adjustment mechanism, are being used here.

MichaelG.

Yeah, there are exeptions to every rule, but you know where i was coming from......a set of bearings off ebay for £5.99 posted direct from xhingyu province, are highly unlikely to be of the same quality as a set of SKF or similar from the local bearing merchants.

Edited By Alan Waddington 2 on 22/09/2018 09:39:39

The far end of the spindle is threaded so I assume the steel collar screws onto that and sets the preload, can't see from the photos how the collar is locked though.

A drawing of old arrangement is found here

**LINK**

What is overall length of old spindle?

I know that one shall not scale from a sketch but?

I don't know if it's the same guy making these but I bought a similar 30.5mm through capacity ER40 head through Myford Bits and it's been running reliably for several years now. I have turned thousands of parts on the big bore conversion and it's a joy to be able to chuck up a 1m+ length of bar when you're making parts from stock that's 20mm or more.

There are 25mm parallel OD Morse 2 Taper Sleeves from ArcEurotrade allowing you run your MT-2 taper tooling in the headstock.

.

I was hoping you would join the discussion, Nick ... I found a post on another forum, which I guessed was from you.

If it's convenient; could you please let us know what bearings, and what adjustment arrangement, are used in the conversion.

Thanks

MichaelG.

Let us guess.

**LINK**

The present headstock bearing hole is approximately 52mm and have been bored out to either 55 or 62mm allowing spindle of either 35mm or 40mm.

Let us asume 40 mm spindle with hole 32mm and bearing outside 62mm.

I have thougth of something like it for upping chineese lathes 180 and 210 sizes

**LINK**

The Roy Milner Gentleman has surely acces to a line borer.

Line up relative to existing 52 mm holes.Bore through 62 mm.Make two spring ring ditches say one mm wide and 2 mm deep and we are in pure Boxford country.

Cheap and dirty and very good

https://www.model-engineer.co.uk/sites/7/images/member_albums/134675/572759.jpg

Edited By Niels Abildgaard on 22/09/2018 18:23:56

It's my assumption that it has just one taper bearing front and another at the rear as it uses a split adjusting ring clamped with a cap screw at the rear of the headstock, I've not had to strip it yet so I don't have bearing details.
If I ever do strip it I might convert my "spare" head too,
Regards,
Nick