Myford Squareness.

If the saddle on a Myford Super 7 is set to face items very slightly concave does it mean...

 

(a) the front face of the cross slide is at a very slight angle?

 

(b) the front face of the cross slide is square to the lathe bed because the dovetails it slides on are at a very slightly angle?

 

(c) are the tee slots of the cross slide at a very slight angle or parallel with the lathe bed shears?

 

It makes a difference if you're using the tee slots to mount a fixture truly parallel with the axis of the lathe.

Myford have a fixture - much like a long angle plate, which uses the relevent vertical shears to reference it at an accurate 90 degrees to the lathe bed, ie. nominaly parallel to cross slide movement. The saddle is then scraped on it's lower vertical guiding surface, so that a dial gauge when affixed to the cross slide, shows a very small positive reading when moved from the front towards the rear of the lathe. So in effect, the whole saddle/cross slide assembly is turned very slightly anti-clockwise when viewed from above, with everything within that assembly being machined at (nominally) 90 degrees and no special allowance is machined into the tee slots or other faces as this in built 'error' is so small.

 

Martin.

Thanks Blowlamp. That's exactly the info I was looking for. Presumably, if one could be bothered, it would take little effort to true the saddle assembly up using the same technique if an occasion demanded it although I'll say right from the word go, I think I can live with it.

Am I missing something Chris, why would you want to alter it and what occasion could possibly demand it. Myford go to a lot of bother to ensure the lathe faces concave for good reason, we are perhaps talking about one thou hollow across the diameter of the large faceplate, in fact most ( decent ) manufacturers set their lathes this way, my trusty Holbrook dating from 1946 faces a gnats concave. It is not a case of living with it, it is how it should be - be grateful.

Baz, context is everything. I'll be grateful when it doesn't introduce an error elsewhere, such as...

 

I'm making an alternative Hemingway tool post that bolts to the top face of the saddle. You lose the ability to swivel the tool post but it's a much more rigid set up that can take heavier cuts than the standard post plus the design is biased towards the centre of the lathe so that it doesn't foul the tailstock. You can get a cutting tool right to the tip of the centre while the slide still operates parallel to the lathe axis which means you can use the topslide dial to advance the tool accurately. It's positioned by means of a strip that fits into one of the tee slots in the cross slide. If the tee slots aren't truly parallel to the bed, the tool won't cut parallel.  My strip fits the slot with no detectable clearance whatsoever (which is what I was`aiming for) so removal and refitting sees it positioned repeatedly accurately. It seems pretty pointless investing huge amounts of time to ensure things are square and well finished if a wonky slot is going to make the entire exercise pointless.  If I could mill the dovetail slides with the base fitted to the lathe saddle, I could guarantee they'd be in line with the bed but it's been mostly machined on a separate milling machine which unsurprisingly specialises in maching things squarely. I may be chasing impossibly tight tolerances but that's the bar I'm aiming at. And no, as mentioned, I'm not about to undo Myford's good work. Living with it is being aware that it's there and allowing for it. Knowing where the anomaly is and what impact it has on the other components is half the battle.

Hi Chris

 

I'm a little confused here. You say that this is a Hemmingway  tool post you are making which fits to the saddle - is this their version of the "Gibraltar" Toolpost? If so I don't quite see where the topslide comes in. You see youv'e got me intrigued now!

 

No, not the Gibraltar type. It's the Improved Topslide. Fairly basic stuff but it's a good addition. Google Hemingway kits, go to tool holding and then under Myford Specific Items, you'll find the Improved Topslide. I just posted a link but it screwed up the page layout so I've edited.

 

I prefer the accuracy and directness of the topslide dial rather than the somewhat wooley feel of moving the saddle via the leadscrew.

 

 

 

 

Hi Chris,

 

I hope I'm not trying to teach granny to suck eggs', but for long addresses, if you highlight a suitable word in your text and then add your link as normal with the icon, it then becomes attached to the word like this. 

 

You can also ask it to open a new window as I did to avoid leaving the page you are on by choosing 'Target' - 'New Window'.   hope that helps in future,

 

Regards

 

Terry