Smart and Brown Model A Fine feed adjustement

[Matthew FursemanParticipant @matthewfurseman25697]

I have very recently acquired a Smart and Brown Model A. Having only previously used a Drummond pre-B this is quite a significant machine to me. I've been wiping the crud off and exploring the functions, however I've come across a problem and am not sure if there is something amiss in the apron or if it user error. I cannot get the fine feed / cross slide feed to engage:

The fine feed bar feels like it rotates freely (when not selected at the headstock), regardless of the position of the lower right lever. I also cannot get the black surface facing knob to move, there's a tiny amount of play but it won't rotate, I'm stuck with the 'O' showing in the window.

My guess is that a gear or keyway has broken and the feedscrew won't engage with the rest of the apron, although I'd still expect to be able to wiggle the black knob around, possibly while feeding the crosslide, so I'm not sure…

Does anyone have any suggestions?

[Matthew FursemanParticipant @matthewfurseman25697]

Issue with the engaging the fine feed / cross slide feed on the Smart and Brown Model A

[Martin ConnellyParticipant @martinconnelly55370]

First off make sure the half nuts are disengaged as there is an interlock to prevent the power feed and screw feed fighting each other. Then the black knob should rotate to either the left or right to engage sliding feed or cross slide feed. It may need some movement of the carriage or cross slide to get it to engage. There is a detent to overcome to turn the knob as well. Once rotated then the other lever (not the half nuts lever) needs to be moved to the working position to make things move.

Martin C

[Matthew FursemanParticipant @matthewfurseman25697]

Hi Martin, thanks, I did give that all a try already, gently wiggling all the slides and also the leadscrew and fine feed 'screw' while attempting to turn the knob and also while engaging and disengaging the fine feed lever. I also tried turning the knob as hard as I could by hand but it wouldn't budge.

[SillyOldDufferModerator @sillyoldduffer]

A similar problem was fixed recently by slackening the saddle holding bolts slightly and waggling. As I recall an over-wind had wedged the internals together enough to stop the controls moving, and allowing a little temporary freedom was enough to break the wedge and restore normal operation.

Otherwise I think the saddle will have to be opened up to see what's causing the jamb. Fingers crossed it's not serious.

Are you able to confirm the half-nuts are open by peering behind/under the saddle? Might need a bit of help with a lever if they're stuck.

Dave

[Martin ConnellyParticipant @martinconnelly55370]

I wonder if the half nut lever (top right) is working properly. Can you move the carriage along the bed by turning the handwheel? Does it lock in place on the leadscrew when the lever is moved?

Martin C

Edited By Martin Connelly on 18/07/2022 18:40:08

[old martParticipant @oldmart]

I know the feeling. The Smart & Brown model A Mk 1.5 at the museum has had the fine feed sort of working for years until about a couple of months ago, when the lever would not engage. The automatic disengagement when hitting the stops for the saddle never did work. So a month ago, we took the apron completely off and partially dismantled it. The leadscrew and feedscrew have to come off at the same time. The parts drawings available do not show everything, unfortunately, so they are of limited help. The correct working of the feedscrew is for automatic disengagement when hitting saddle stops in either direction, but as there are no stops on the cross slide other than running out of movement the onus is on the operator to stop before that happens. We spent many frustrating hours making the limited adjustments and I have fitted a weaker spring to the cam mechanism for the worm drive. I know exactly how it should work, but that is not enough to actually get the ancient design actually working. There is an interlock to prevent the leadscrew nut being engaged at the same time as the feedscrew mechanism, and vice versa. One thing I found was that the hinged part with the worm, cam and spring was dropping down too low for the lever to be able to raise it without help. Shimming the block which is bolted to the base of the apron solved that, but the height of the flat part of the ramp which holds the worm gears together must be lowered an equal ammount to the shim thickness. Be prepared for a long slog to get things right, and while you are about it, replace any bushes and shafts which are worn. The picture only shows half of the total number  of gears in the apron, the others are hidden.The selector mechanism for changing from saddle or cross slide is right in the centre of the apron, behind the worm gear.

Edited By old mart on 18/07/2022 19:24:28

Edited By old mart on 18/07/2022 19:25:39

[HacksawParticipant @hacksaw]

On the subject of S&B ,if i could interrupt …On a Model M fine feed , how do you trigger it off ? Am i missing an adjustable " Stop" ? Or is the onus on the operator to hit the knob down just in the nick of time ?( which is what i do…) Also what are the knurled parts for either side of the apron where the power feed axle enters and exits ?

[Martin ConnellyParticipant @martinconnelly55370]

This is from memory so may be a little bit erroneous. There is a clutch in the apron. When it comes up against a stop it slips. I think it is based on spring pressure and the large circular item you can see around the drive shaft in your picture is an adjuster that increases or decreases the pressure. When it comes up against a stop there is a loud ratcheting noise. There should be an adjustable stop that clamps to the centre of the bed and on the carriage there are two small hardened pins either side that bear on it. There is also a conical clutch for the drive that is engaged when the brass knob at the bottom centre of the apron is pulled up. This can also slip under excess load so acts like a torque limiter.

Martin C

[Matthew FursemanParticipant @matthewfurseman25697]

I wonder if the half nut lever (top right) is working properly.

I can see the half nut around the side of the apron, it engages and disengages nicely. You do of course have to catch the thread right.

The Smart & Brown model A Mk 1.5 at the museum has had the fine feed sort of working for years until about a couple of months ago, when the lever would not engage … we took the apron completely off and partially dismantled it.

Oh dear, I'd hoped not to have to do that. There's the bolts around the front plate, can you remove the handles and leavers and then take the front plate off the apron without removing the lead and feed screws?

The lockout between lead and feed seems to kinda work, I can lift the feed lever and it clonks into place, if I then push the leadscrew leaver it drops the feed lever back down.

When the leadscrew's engage I can't toggle the feed lever.

I tried slackening the bolts through the top of the saddle and wiggled things about with no change. I removed the black handle, the play I felt was only in the handle, the shaft doesn't seem to turn at all. I assume that the casting behind it comes off but it didn't want to budge from a gentle tap.

[old martParticipant @oldmart]

You can remove the apron cover with care for assessment.

Remove the leadscrew lever, one grubscrew, woodruff key and slacken off the threading dial friction adjuster (that grubscrew shown in the picture, then remove the dial). Remove the fine feed lever (taper pin small end at bottom). Remove the main wheel and woodruff key which moves the saddle. There are 5 SHCS holding the fromt on and when they are removed, carefully use a thin blade to work it off the dowel pins. The 2 dowels are top right and bottom left. If you do need to remove the plate at the bottom, make sure that the front lefthand screw is the short one, as it intersects with the screw holding the front on.

Post a picture of the mechanism.

[Matthew FursemanParticipant @matthewfurseman25697]

Posted by old mart on 20/07/2022 09:31:09:

You can remove the apron cover with care for assessment.

Remove the leadscrew lever, one grubscrew, woodruff key and slacken off the threading dial friction adjuster (that grubscrew shown in the picture, then remove the dial). Remove the fine feed lever (taper pin small end at bottom). Remove the main wheel and woodruff key which moves the saddle. There are 5 SHCS holding the fromt on and when they are removed, carefully use a thin blade to work it off the dowel pins. The 2 dowels are top right and bottom left. If you do need to remove the plate at the bottom, make sure that the front lefthand screw is the short one, as it intersects with the screw holding the front on.

Post a picture of the mechanism.

Thanks! It may be a few days before I can get around to it, work is busy and I'm babysitting this weekend. Do I need to drain the oil before pulling the plate?

[old martParticipant @oldmart]

Just put a little tray underneath, the capacity is about a cupful, yours will probably not have any. When reassembling, you only need sealant along the bottom and a couple of inches up the sides. Check the worm gear shaft for straightness, it comes out easily. We did a major rebushing and also made several new shafts also Mike got the oil pump working. That pump oils the saddle and cross slide as well as the leadscrew nut and all the shafts and bearings inside the apron. Do you have the parts drawings?

Edited By old mart on 20/07/2022 21:33:17

[Matthew FursemanParticipant @matthewfurseman25697]

Hi, sorry it's been a while; I've still not taken the apron apart but will soon I think. I've got a stack of original manuals and parts drawings and a brochure for the Model A, I'm happy to scan them to a pdf and upload if that's allowed and there's a demand for them.

I've also found the sheer pin on the first change gear had snapped when I looked under the cover, so need to make/source one.

[old martParticipant @oldmart]

The sheer pin dimensions should be in the manual, 1/8" mild steel would do, make a couple while you are about it. The drawings do not show everything there is in the apron, and it takes some doing to understand how things work inside. Both fine feeds are powered by the feed shaft, through the universal joint to the worm and the worm gear. Then the gear change with the arrows horizontal runs through to the rack which moves the saddle, (carriage) or 0, out of gear, to vertical arrows which run through a gear train to the cross slide leadscrew. The worm is held in place by a spring loaded cam which can move to the right if there is resistance to the saddle moving, (hitting the stop in either direction) The movement of the cam to the right disengages the drive. This feature is not intended for use when facing, only axial turning. This automatic disengagement is difficult to achieve, but the fine feeds can be used without relying on it if you are careful.

[Matthew FursemanParticipant @matthewfurseman25697]

I finally returned to this after quite some time as I was doing some cleaning on other parts of the lathe and stripping my mill spindle (thanks Old Mart for your help in that thread!). The inside was filthy, without about 1cm of gunked up oil with shards of bronze and steel mixed through it. I think the pump on mine is working as I get a smear of filthy black oil over the ways when moving the apron back and forth. The brass dog on the gear selector was stuck solid, presumably glued by the dried out oil. I removed it, soaked in WD40 overnight and then took it to a vice with grips and freed it.

I've cleaned everything a lot and it's now looking pretty good, ready to go back together! I haven't run the lathe under power yet so not sure if the clutch works, I didn't get a micrometer stop with the lathe anyway. I've got a bunch of other problems to solve which I'm working through as I do this 'functional restoration' of the thing, not sure if I should start a new thread or keep asking away in this one.

[old martParticipant @oldmart]

The ends of the shafts look unworn, I had to make some new ones as well as rebush everything. The trip mechanism to the lower right is a nightmare to get working properly, our lathe at the museum actually works after 15 years. The adjustment is very old school, all knowhow and no easy adjustment. You ought to remove and clean the pump while the lot is dismantled, it is lower left, with a cover plate underneath.

[Martin ConnellyParticipant @martinconnelly55370]

I have a micrometer stop but it is not a great design. The slightest bit of debris makes it very hard to adjust and it is actually prone to slipping when power feed pushes the carriage against it. Often dropping a suitable length of bar between the headstock and the carriage to give a positive stop to work up to and using the compound feed for fine adjustment is the best option. Let me know if you want any pictures of it to work out if you want to make your own.

Martin C

[old martParticipant @oldmart]

I made two stops for the model A for either side of the saddle (carriage) with 20tpi screws in them and wheels with 50 graduations around them for 0.001" adjustments. The fine adjustment screws never get used. Making them is easy if you have a mill, otherwise not. Before the fine feed was working correctly, the saddle would push the locked stops along without disengaging, anything solid will immediately cause damage to the shafts and gearing inside the apron.

By all means use the fine feed, but disengage it manually before hitting anything. Try the facing first, nothing bad should happen if you go past the centreline. Always check first which way the saddle of cross slide moves before setting up a cut. There are no stops on the cross slide, so manual disengaging with the lever must be done. If using the fine feed with the saddle to a shoulder, set to cut away from the shoulder is safer than towards as there is no danger of a pile up. Hitting a shoulder with the tool before trying to disengage the feed lever will end in tears.

Edited By old mart on 17/10/2022 17:51:43

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