Lathe threading gear box hard to shift but free off the machine, Harrison M300

Harrison M300. The threading quick change gearbox has one knob which has 8 positions. It can be hard to get into some of the positions. I have run solvent in the box and drained/ refilled. which has helped. These gearboxes are known for gunk building up on a cam which shifts forks to slide gears around. This cam is what the knob in question moves.
I have had the apron and headstock open and their gears etc look very clean just a slight sludge on the bottom is all. What I can see of the threading gearbox ,from the oil fill, looks the same to me.
I took off the gear that connects the QC box to the headstock gearing. Now the qc box changes fast and smooth with no sticking at all. Seems like I do not need to drop the QC box since it is fine by itself? Something is hanging up when it is connected to the main gearing but I do not see how.
All this shifting is done with the motor off and just rolling the chuck as needed. I tried with the motor running and it did not free up anything. Once I pulled the gear I did rotate the input shaft as needed to shift the qc box. I will have to check all the idler gears for junk in the teeth or something now.
Bill D.

The Harrison Yahoo group has nothing on these symptoms

Have seen a cheapo import gall the sliding shaft and blow apart a QC shifter due to lack of lube. Have also seen bent shifter shafts. If it seems worse when mounted, wonder if it is the box machined out of square and causing binding? Might bolt it up finger tight, then start bringing each bolt up snug in tiny increments in a star pattern. If you find when and where it binds, might just need a little shim to line it all up right.

On the 250 there is a washer there - does the gear train spin freely ? It needs to or w/out a small movement the gears won't engage. Not nicely,anyway.

I lied in the title to make the problem easily understood. I have not actually removed the box just the one gear on the input shaft. It looks like the previous owner may have remove the box because there is blue silicone sealer that ozed out in spots. This was made with paper gaskets so the silicone was done later. I suppose it could be cockeyed with the drive train, but the output shafts to the apron spin fine with handpower input to the QC. The input gear was rather hard to pull so maybe it is misadjusted. I thought it was just a old tight fit. It is a fiber gear and I did pull it by hand. If they removed the paper gasket it would bind the gears together.
Bill D.

That is a half ass repair. You need to find out the thickness of the original gasket to put the pieces in the proper positions.

I have one of those lathes and find that numbered dial doen't always want to go to the number I need with out a little help. I just grab the feed rod with my fingers and give it a turn while shifting? I don't think it's any different than any other machine tool with sliding gears and certainly wouldn't waste any time trying to improve it.
Dan

Dan, this was beyond being able to shift it into some gear ratios at all even with rolling the chuck. But it would randomly be hard to shift into a gear or two. but not always the same gear and often two gears numerically next to each other. Like one day I could not get it into 3 or 4. Next day they might be fine but 7+8 would be impossible to shift into from either direction. The DPO drilled a hole in the shift knob and inserted a 6" long bar to force the knob to turn.
Bill D

As td says, it's got the gear clearances screwed up. It may have half the gasket on and half off, inducing the bind I suggested. Clean it off, put a proper thickness paper gasket on it and I'll bet it clears the problem right up.

Mike C. said:

As td says, it's got the gear clearances screwed up. It may have half the gasket on and half off, inducing the bind I suggested. Clean it off, put a proper thickness paper gasket on it and I'll bet it clears the problem right up.

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I think your way off on the gasket idea. The gear clearances are set in the box, has nothing to do with the mounting to the bed or the gasket thickness? The banjo sets the end gear clearances and would probably still do so if you machined a quarter inch off the gasket surface. About the only thing the gasket thickness would affect is the lead screw/feed shaft alignment with the bed.
Bill D.
You might need to get into the gear box and take a look around. I bought my lathe new in 1990 and never had any issues with the QC gearbox. I will admit that I never noticed any gasket sealer that oozed out of the sealing areas so maybe someone was in there and did a botch job repair before you got it?
Dan

Danny, I understand that the gear clearances for the change gears themselves are in the box, but if the box is being twisted out of shape by a half missing gasket, it could be enough to bind. Also, if there are gears driving or driven by gears on the ends of the box, or shafts going in or out of the box, those could be out of alignment. Being somebody has been in there, could be they bound it up by crashing or engaging leadscrew and feed at the same time and bent hell out of something, too. May be the only way to get it to release was to pull the gearbox.

tdmidget said:

That is a half ass repair. You need to find out the thickness of the original gasket to put the pieces in the proper positions.

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Support the g'box on matches and tighten the screws while clocking the feed shaft both ways ( horiz and vert ). If the feed shaft binds it can be hard to select gears. I do have a gasket somewhere - I'll try find it and measure the thickness.

I have had problems with mine and ended taking the box off and cleaning it out.
The gear shifters are a bit sensitive and can jam or fall out of engagement, the detent onthe knob gets gummed up and can allow the gears to stop driving.
I take mine off every year or so and give it a good clean.
The alignment is not too sensitive.

Just brought a second M300 home, Ebay "Pig in a Poke" deal meaning sight unseen. I remembered this thread and thought I'd add to it.
The machine is a lot newer than the one I already have and looks like it's in very good shape except that numbered knob was froze solid. I was at a point where I had most of the mechanical things sorted out, oil change to the head stock and apron, cleaned the built up crud off the ways and even got it reasonably level but was at a loss on that binding knob (also an electrical problem to sort out). I decided to fill that gear box with kerosene and see what happens, figured it might even clean the sight glass? I did the fill at about lunch time, about 5:30 it was on my mind and went out and started playing with it. A little twisting by hand and it suddenly moved, a little more twisting and rotating the spindle it finally went through the whole range. What a great feeling to get that freed up without a tear down, especially since I don't have the proper manual for it and I hate buying parts if unnecessary.
We got snow here yesterday and it's in an unheated garage so I think I'm going to leave the kerosene in it soaking until it gets a little warmer, maybe it will clean that oil sight glass like new.
Looking into this the one manual I have shows a gasket between the gearbox and bed, the picture seems to show that it only seals the bottom and both ends? It looks as if the head stock overlaps the top of the QC gearbox but doesn't show a seal there so might allow someone sloppy with the coolant to get some in it?
Dan

Yes they are known for coolant seeping from that top gap. the delrin cam swells with water and makes them hard to shift. I found when I reinstalled the drive gear the box was easy to shift now. My theory is the six way? hub is not perfectly centered and I randomly installed the gear and it has a better clearance now. I have marked it now so it will reinstall the same way next time.
make sure to pull the idler gear on then bango. It has an oil hole in the end. When I pulled mine I found the oil passage was plugged with dry grease and no oil was going to the bearing surface. Quick and easy job with a big crescent wrench.
Bill D.

T. S. Harrison & Sons, Ltd. - Publication Reprints - Harrison M3 Machine Manual | VintageMachinery.org

3 years later it is still shifting fine. I do not use coolant just brush some oil on. I ended up taking the gearbox off and washing it with solvent and brushing every gear tooth and shaft. It had looked clean but the few hours spent with a small brush made a visible difference. While I had it open I replaced the oil sight glass.
Bil lD