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Super 7 Leadscrew

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Nick Taylor 223/01/2017 10:39:29
102 forum posts

Morning Gents,

My Super 7 odyssey continues!

With many thanks to this forum my new-to-me Super 7 is really coming together. I'm slowly working through the niggles I find.

My newest question is how to remove the leadscrew? I want to inspect, and probably replace the oilite bushes as it turns well but there are tight spots and plenty of crud being expelled from the oil nipple whilst running at speed.

I also have a problem with the alignment. My lathe has a narrow guide saddle on a wide bed. The saddle has been machined to allow it to run on the rear shear (so I'm told). Now the saddle moves perfectly, there is no tightness or slop but obviously the half nuts are not where they should be, and there is visible deflection on the leadscrew when the nuts are engaged.

I’m assuming it will be easier to mod the leadscrew mounts rather than dismantle the apron and try to shim the half nuts?

Thanks in advance,

Nick

KWIL23/01/2017 11:46:41
3563 forum posts
70 photos

On the S7, the leadscrew nut is opened and closed by cam pegs which engage with cam that operates them via the ball knob lever.

This is all enclosed in an eccentric sleeve which is locked by half dog set screw on the left hand side of the apron. Slacken this and rotate the sleve to better centre the half nuts.

If this is not enough, then someone has removed metal from the bearing faces of the carriage.

Martin Kyte23/01/2017 11:48:04
avatar
2797 forum posts
53 photos

I am assuming you are talking about a leadscrew deflection in the horizontal plane

I would think that shimming the apron would be the way to go for horizontal alignment. The nuts are adjustable in the vertical plane

regards Martin

KWIL23/01/2017 12:01:46
3563 forum posts
70 photos

In the OP, 5th para, he says the saddle has been machined to allow the use of the back edge of the rear shear.

Was this by machining off the narrow guide? If so, I guess the whole saddle will have moved forwards, so yes, as Martin says, horizontal misalignment?

If this is so, I personally would not vary the leadscrew bearing mountings, but interpose a spacer/shim to whatever is running on that rear edge.

Edited By KWIL on 23/01/2017 12:05:07

Nick Taylor 223/01/2017 12:11:59
102 forum posts

Hi, thanks for the replies.

Sorry I should of been clearer - Martin is correct, the movement is horizontal, i.e the lead screw is moving away from the bed when the half nuts are engaged.

I'll get the DTI out later on and measure exactly how much, then I think I will look at shimming the leadscrew brackets. How do I remove the leadscrew?

Cheers,

Nick

Nick Taylor 223/01/2017 19:13:50
102 forum posts

Just had a poke with the DTI, lateral movement away from bed of 0.45mm when closing the half nuts!

Robbo24/01/2017 10:28:11
1504 forum posts
142 photos

Nick

My own Super 7B has had the saddle modified, as detailed by J A Radford in ME 3418, to bear on the rear shear instead of inside the front one.

When he had finished, he found a misalignment of 1/32" of the leadscrew/apron. (Imperial in NZ in 1971). About 0.7 mm (I think smile p   ) so more than yours.

He cured this by slackening off the capscrews holding the apron to the saddle, engaging the half nuts and then tightening the capscrews. There was enough play in the capscrew through holes in the apron to take up this discrepancy.

Probably worth trying before messing with the leadscrew, moving which will maybe upset the engagement of the changewheel at the L/H end.

 

 

Edited By Robbo on 24/01/2017 10:33:57

Martin Kyte24/01/2017 10:58:22
avatar
2797 forum posts
53 photos

That sounds like the answer Robbo. In my earlier post I stupidly was thinking (from memory) that the apron bolted to the front face of the saddle not the underside. It's the only sensible way of building the lathe to take account of variations in the position of the saddle due to wear/regrinds etc. It's without doubt the way that the lathe should be assembled. Clamp the leadscrew up then tighten the apron bolts, same as refitting the leadscrews on the cross slide or the topslide where you screw the leadscrew in fully before tightening the endplate bolts.

regards Martin

John Haine24/01/2017 11:19:20
4717 forum posts
273 photos

When I had a problem with the saddle alignment on my new S7, Mr. Townsend of Myford described the process that Robbo mentioned above, with the addition that to do this you should move the saddle to the extreme RH end of the bed.

The leadscrew brackets are simply bolted to the bed with capscrews, but there's also a couple of alignment dowels that need to be removed. To get these out you need a long 4 BA (I think) bolt with a small weight made from a scrap of steel bar with a clearance hole drilled through. You thread this on the bolt, screw the sharp end into the threaded hole in a dowel, and slide the weight sharpish against the bolt head a few times. Then you need to remove the handle, make sure the halfnut is open, and pull the leadscrew out through the hole in the LH belt cover. As I recall it was easy to remove - I did this to mill a flat on the RH end to fit a timing pulley when I did my CNC conversion.

Shimming the brackets shouldn't cause a problem with the change gear as it's the leadscrew that sets the position and there's lots of adjustment in the banjos to take up any slack.  (Later edit - at least small shims!)

Edited By John Haine on 24/01/2017 11:24:25

Nick Taylor 224/01/2017 11:56:20
102 forum posts

Hi Gents, thanks for the replies.

I managed to strip everything down last night, I completely removed both support brackets and the leadscrew.

Tailstock end bearings are in great shape, looks like someone has installed a DIY attempt at the thrust bearing modification to eliminate the lash in the leadscrew, consists of some nicely finished bronze shims and works nicely.

The headstock end bearings are bad, scored and are worn out of round by nearly 3 thou so these will be replaced. I think the issue is someone has pressed the bearings right up to each other and there is no oil channel between them. So… make or buy? I’m tempted to make seeing as the parts from Myford will be £12 and for £30 I could buy enough Oilite cored bar to replace every bush on the entire machine!

Leadscrew is in good condition and the half nuts look new, they’re also setup well. So, I cleaned everything up and reassembled fitting 0.5mm shim between the brackets and bed. Less than 0.15mm leadscrew deflection now however it does get slightly worse the closer you are to the tailstock so I will go with Robbo’s suggestion later I think and see how that works out.

I need to adjust the under-strip shims at the front of the saddle as well as there is a tiny bit of lift showing. So, the saddle may be coming off anyway in the next few weeks.

Again, gentlemen I would like to thank you all for you replies, I’m slowly learning and I thank you for sharing your knowledge.

Cheers,

Nick

DMR24/01/2017 12:05:56
128 forum posts
14 photos

I had this when I decided to take advantage of a VAT free bed regrind offer that coincided with a (real) Myford open day that I intended going to anyway. This was about 12 months before Chris Moore sold out. To cut out a lot, I needed a replacement saddle and dully collected the bed with nothing specifically said to me. I soon realised as I rebuilt the machine that the saddle was ground to the newer wide bed pattern which I thought a bonus!

The lead screw and gearbox were left to last in reassembly after ensuring that all else was well. So I was not amused to find that the clasp nut did not align with the lead screw by quite some distance. A call to Myford and a chat with Malcolm eventually revealed that the stock of early saddle patterns was exhausted and history/retirements had forgotten why all regrinds were not performed to the more modern pattern.

I was asked at the time not to make this public in a very nice way by some favourable moves on my behalf, including two more 60 mile trips to Nottingham and back. A further replacement saddle was found (I didn't ask where from) and the whole job came out right in the end.

I have to say that, remembering how far my clasp nut was out of alignment by eye, Nick has an impossible task if the saddle he has is of a later pattern. This was presumably to do with the later introduction of PCFeed.

Sorry Nick

Dennis

Robbo24/01/2017 12:48:25
1504 forum posts
142 photos

John is right in saying move the saddle to the right hand end of the bed because this is where minimum wear takes place. If you remove the tailstock then no wear on the outer vertical surfaces of the bed.

Forgot to include this in previous post - old age and senility strike again!

Nick Taylor 224/01/2017 12:55:39
102 forum posts

Hi Dennis,

I think angular alignment is more of an issue than the lateral position now, looking at the leadscrew deflect when I close the nuts I think Robbo's suggestion should remedy it.

My saddle is an older narrow guide style, but the bed is a slightly later hardened PCF example. I’ll try Robbo’s suggestion if I can get in the workshop tonight and see how I get on, I might take the apron off and set the under-strip shims as well while I’m at it, see how I do for time.

Cheers,

Nick

DMR24/01/2017 13:28:08
128 forum posts
14 photos

Hi Nick,

I accept that you do not have the combination of bits that I had. In fact just the reverse. I fail to see how your error could be an angular thing , but then if the error is greater at one end of travel than the other, then so be it and shims will correct it. However, if you should ever try to fit a gearbox, I think your problems will compound.

Good luck,

Dennis

Nick Taylor 224/01/2017 14:05:46
102 forum posts

Hi Dennis,

Yes, I agree not having a gearbox is saving me a lot of trouble here and allowing me to get away with just shimming. I think the idea of loosening and re-aligning the apron will solve the little remaining deflection I have. Looking down the leadscrew whilst closing the nuts you can see the tailstock end of the nut is making contact before the headstock end yet I have clocked the leadscrew to the carriage and they are running true to each other.

Like you say if I want to fit a gearbox a later date then I'm going to have bigger problems.

I’ll report back later!

Cheers,

Nick

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