Harrison M300 screw feedbox issue

[scottmk1]

OK cool. I guess he maybe had a few spares on the bench

 

[Welderpaul]

I don't have the X position on this feed gearbox, something nasty going on as it works in W and Y positions but flops about inbetween - the lever can be moved even when the feed shaft is turning. I'll whip the gear box off tomorrow and see what nastiness is in there.
Do the three shafts to the right hand side of the gear box come off easily enough?

Anything to be aware of?

 

[RobCox]

It comes off easy enough. You'll have to remove the block on the far end of the bed.
Don't forget to drain the oil out first!

 

[Welderpaul]

Thanks Rob

 

[RobCox]

I took mine off when I tarted up my M300 a couple of years ago. I took a load of photos of the inside of the box with the 1 to 8 selector in each position. Also I have a spreadsheet where I worked out the thread pitch that each setting generated. These are for a 4 TPI leadscrew. If any of this is any use, PM me and I'll send you the info.

Rob

 

[Welderpaul]

Thanks Rob, i'll get my head into it tomorrow afternoon and give you a shout.

 

[Shox Dr]

I took mine off when I tarted up my M300 a couple of years ago. I took a load of photos of the inside of the box with the 1 to 8 selector in each position. Also I have a spreadsheet where I worked out the thread pitch that each setting generated. These are for a 4 TPI leadscrew. If any of this is any use, PM me and I'll send you the info.

Rob

Why? Didnt have a thread pitch info plate on the front?

 

[RobCox]

Why? Didnt have a thread pitch info plate on the front?

The thread pitch chart was there. Battered, but legible.

The spreadsheet was done in a bored morning at work, purely out of curiosity for how close the designers had got the metric pitches given that there's no 127 tooth gear in the chain. Its mighty impressive given that this must have been hand calculated, no CAD back then.

The pictures of the inside of the box were to make sure the 1-8 knob was lined up properly, in case I needed to take the spindle with the cylinders on out. The divot for the grub screw on the 1-8 dial is chewed on mine, so it wasn't guaranteed to line up when reassembled. They've been useful since to someone who's had a box apart and needed to know which order the cylinders go back in to get the selector to work properly.

 

[Welderpaul]

Took the gear box off with no dramas. Fairly clean inside with no wear on the gears, no chips or bits missing. (Maybe I have found the holly grail of a lathe that actually has been 'lightly used, ex college'?) This is the first time its seen daylight inside since the late 70's when it was made. The little slugs out of the paper gasket bolt holes were floating about in the bottom of the casing.

The problem is that the selector lever indent positions don't line up with the gears inside. Whilst the selectors are tight on the shafts they are in the wrong positions. Someone has then wound the pressure right off on the detent pressure so the levers were slack. It was pot luck which gear you picked up, and in most positions where the detent engaged the gears were half/half engaged. Suprised there wasnt any damage.

Easy enough to line the gears up inside and match up the selector levers, tighten then sort out the detents.
There's no detent at all on the 3rd lever. I have a 5mm ball bearing, the M6 grub screw, but no little spring so annoyingly the gear box will have to wait to go back on.

The gasket came off in more or less one piece but i will scrape it all off and replace. it will be a pain if it weaps once all the bits are back on. What sealant should i use? It looks very much like cured rubbery clear silicone rather than traditional gasket compound and was generously applied.
Will probably have to make a gasket.

Need to find a selection box of springs cos the part number (SG353) doesnt give any clues.

 

[Agroshield]

The spring will be less than 5mm dia. or it will argue with the minor dia. of the M6 threads. Maybe 10mm long if it is drawn to same scale as the grubscrew.

Spring out of a pen (biro) would probably do.

Blue Hylomar.

 

[Brad93]

You may find a detent ball grub screw is better and more adjustable to replace the spring.

 

[RobCox]

I made a gasket from nitrile bonded cork. I used the same material for the bottom of the apron.

Hasn't leaked yet and has been like that for 2 1/2 years.

 

[Welderpaul]

Ordered a 4.8mm dia spring, should be ok cut down to suit. I can't get the others out to check against them without damaging the thread so i'll leave them alone.

 

[Welderpaul]

Whilst it was off i sorted these bits out. Fixings were all chewed up so retapped the threads, chnged the fixings and gave them a clean. What do they do? Seem complicated things

 

[RobCox]

Thats your safety mechanism. If you crash the lathe they should slip and prevent catastrophic damage.

 

[Shox Dr]

As far as Im aware the screw curting box on a M300 did NOT have a gasket. Interesting to see yours did, Paul

 

[Welderpaul]

Thats your safety mechanism. If you crash the lathe they should slip and prevent catastrophic damage.

Realised that’s what was being discussed above

The washers in these seem extremely flat and tired. Another thing to sort.

 

[Brad93]

Realised that’s what was being discussed above

Yep those are your Belleville washers.

obviously you only want the screw turning/engaged when you’re actually screw cutting, so you should be able to pull that top one back to disengage the screw. Well it works like that on my older 140 anyway.

 

[RobCox]

Yep those are your Belleville washers.

obviously you only want the screw turning/engaged when you’re actually screw cutting, so you should be able to pull that top one back to disengage the screw. Well it works like that on my older 140 anyway.

On an M300 the WXY knob disengages the leadscrew in the X position for turning and facing.