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Warco lathe feedscrew shear pin

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petro1head23/01/2020 13:16:05
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714 forum posts
141 photos

I have the wm290, any idea what i need to buy to replace the shear pin ie dia and material

Mick B123/01/2020 13:51:44
1346 forum posts
75 photos

On my 250V, it's 1/8" or 3mm standard brass. Think that's all I've ever seen on any normal lathe.

SillyOldDuffer23/01/2020 14:17:50
5119 forum posts
1073 photos

I can't remember the diameter of the pin on my WM280, but it was about 3mm, not tapered. Whatever it was, the hard part was getting the broken pin out. With the feed-screw fitted to the lathe, I couldn't see the broken pin well enough to drive it out - high risk I was uselessly hammering the screw rather than hitting the pin. With the screw off the lathe and everything in plain view it took about 10 seconds to tap the pin out and measure it.

No problem turning 4mm brass rod down to size by hand with the lathe in bits. Then it was straightforward to tap the pin in when the feed-screw was re-fitted.

Assuming your 290 is like my 280, the awkward bit will be removing the bearing block at the tail end to get the feed-screw off. (If you have to; with luck you can see the old pin and remove it in-situ.) Mine is held in place by two bolts (easy) plus two dowels (tricky). The plain dowels take an Allen Key but they're sort of shimmied out rather than unscrewed. I may have done it wrong by turning with a pulling action with the Allen key tilted to get a bit of grip. Bad language didn't help other than making me feel better. Reassembly is easy - they just slide in.

Dave

petro1head23/01/2020 17:41:20
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714 forum posts
141 photos
Posted by Mick B1 on 23/01/2020 13:51:44:

On my 250V, it's 1/8" or 3mm standard brass. Think that's all I've ever seen on any normal lathe.

I have bought some of both, thanks

Mick B123/01/2020 18:59:04
1346 forum posts
75 photos
Posted by petro1head on 23/01/2020 17:41:20:
Posted by Mick B1 on 23/01/2020 13:51:44:

On my 250V, it's 1/8" or 3mm standard brass. Think that's all I've ever seen on any normal lathe.

I have bought some of both, thanks

Ah. I'm not sure it actually matters which... blush

old mart23/01/2020 20:49:29
1075 forum posts
109 photos

The lathe I use has a drawing for the shear pin in the manual, I have made a small quantity as they are waisted. When I was cutting a coarse ACME thread on the lathe which meant overdriving the gearing and big cuts, I bit the bullet and fitted a solid pin. the forces were great enough to cause a serious risk of the pin shearing during use from the forces and causing more damage that way. It was replaced with a standard pin as soon as possible.

Howard Lewis23/01/2020 22:10:27
2699 forum posts
2 photos

On my BL12-24 (Warco BH 600 or Chester Craftsman) I replaced the original rollpins !!!!!!!!!!!!!!

by 5 mm brass, drilled through 2.5 mm.

better to have the pin shear than damage the gear train! Even more important if you lathe has plastic gears, or maybe they ARE the weakest link, by design?

Howard

Bruno Taylor24/01/2020 16:53:46
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42 forum posts
14 photos

Hi,

I have a WM250V. The sheer pin is brass 3mm dia. Problem is in my case that it does not shear. Through carelessness the other day l locked up the carriage against the stop. The pin did not shear and the result was the carriage pinion shaft bending. This has happened twice now.

Okay it's a quick fix (the second time!!) Remove the carriage gear box and hit pinnion shaft with a hammer. After the first time l decided to fit a plastic shear pin. Will definitely actually do it this time.

Anyone else had this happen?

Mick B124/01/2020 18:43:45
1346 forum posts
75 photos
Posted by Bruno Taylor on 24/01/2020 16:53:46:

Hi,

I have a WM250V. The sheer pin is brass 3mm dia. Problem is in my case that it does not shear. Through carelessness the other day l locked up the carriage against the stop. The pin did not shear and the result was the carriage pinion shaft bending. This has happened twice now.

Okay it's a quick fix (the second time!!) Remove the carriage gear box and hit pinnion shaft with a hammer. After the first time l decided to fit a plastic shear pin. Will definitely actually do it this time.

Anyone else had this happen?

You don't need to take off the gearbox if you've got a standard crowbar with a shallow-bent toe end. You run the saddle to the tailstock end and find the tight spot - that's where the bend in the pinion shank's forcing it hard against the bed rack. Set the tiptoe of the crowbar against the top of the pinion shank with the top of the shallow bend against the corner-pad under the LH near side end of the saddle, then lever up. That bends the pinion shank downwards, away from the bed rack - solving the problem.

My shearpin didn't shear because it was silver steel or something like it. What did shear was one of the keyed bushes in the headstock geartrain, between two paired gears. The shearpin's now brass, but now that you've told me it's still too strong to save the carriage pinion, I think I'll weaken it further at some convenient time...

smiley

petro1head25/01/2020 09:00:22
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714 forum posts
141 photos

Having read about brass shear pins not breaking maybe I sould make an alluminium one

Howard Lewis25/01/2020 14:43:38
2699 forum posts
2 photos

When I jammed my Saddle against the Headstock, the rollpin ensured that the pinion and its shaft bent.

Obviously a regular happening since Warco could supply from stock, at a total cost approaching £70. I cut my own 13T gear, eventually, having found that the chart for the HV6 had errors, including, of course, the one for 13 divisions!

16mm Silver Steel from Cromwell Tools, (£12 ), a 1.5 Mod cutter from RDG (£22 ) and we were back in business, after a few days. Then made the 5 mm OD, 2.5 mm ID, shear pins. Not needed since, Thank Goodness!

Howard

Clive Foster25/01/2020 16:04:00
1987 forum posts
73 photos

It is often advocated that a shear pin be necked with two Vee grooves of centre spacing equal to the diameter of the inner shaft. Especially if steel pins are used.

It is said that the neck provides a stress raiser ensuring that the pin shears cleanly and the tapers prevent the broken end smearing between the inner and outer shafts. Smearing can can create considerable friction between the two parts making it a right pain to align them so the pin can be driven out.

Indeed I have seen one such where the pin had clearly been broken for some time but the smeared and jammed up ends continued to provide approaching adequate, albeit not completely continuous, drive between the two parts. Leaving a right mess when the parts were eventually separated by longitudinal movement.

Clive

Mick B125/01/2020 17:01:51
1346 forum posts
75 photos
Posted by Howard Lewis on 25/01/2020 14:43:38:

When I jammed my Saddle against the Headstock, the rollpin ensured that the pinion and its shaft bent.

Obviously a regular happening since Warco could supply from stock, at a total cost approaching £70. I cut my own 13T gear, eventually, having found that the chart for the HV6 had errors, including, of course, the one for 13 divisions!

16mm Silver Steel from Cromwell Tools, (£12 ), a 1.5 Mod cutter from RDG (£22 ) and we were back in business, after a few days. Then made the 5 mm OD, 2.5 mm ID, shear pins. Not needed since, Thank Goodness!

Howard

Here's the crowbar fix to the bent pinion. Pic 1 shows the end of the crowbar to use, pic 2 shows it in place with the chisel toe on top of the pinion shank and the fulcrum up under the saddle corner pad:-

crowbar fix 1.jpg

crowbar fix 2.jpg

You have to be able to get the saddle far enough from the headstock to get room for the crowbar, and get the highspot on the pinion at the top, ie. where it binds tightest against the rack, so a *very* severe bend might not be fixable this way. But if it's possible, it costs nothing but a minute or two's time - though to be fair, we got the crowbar for free because the previous house-owners left it in a cupboard...

Edited By Mick B1 on 25/01/2020 17:03:06

Howard Lewis25/01/2020 17:34:43
2699 forum posts
2 photos

My pinion shaft was too badly bent to be tweaked back into position. The original material seemed to have more in common with plasticine than steel, having bent inside and outside the Apron. The lathe now runs with a mild steel pinion, Loctited and pinned, on a Silver Steel shaft, located by a brass sleeve. Seems to travel a bit more sweetly, so possibly reduced the backlash during the repair. It won't happen again, I hope, The pinion now disengage from the shortened rack just before Saddle / Headstock contact. So with hollow brass shear pins, and disengagement, there should be no more damaging collisions, unless I omit to open the half nuts at some future time!

Howard

Ian S C26/01/2020 10:51:35
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7467 forum posts
230 photos

Early in it's life I brokethe shear pins on the lead screw of my Tywanese lathe (there are two in tandem). I replaced them with bits of 1/8" brazing rod, about 25 years ago.

Ian S C

petro1head27/01/2020 10:07:22
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714 forum posts
141 photos

I have made an alloy shear pin instead of the brass one

Clive Foster27/01/2020 10:59:45
1987 forum posts
73 photos

petro1head

I hope you put grooves in it to define the shear point and prevent smearing if it breaks. Alloy tends to be rather ductile so it will bend and stretch before shearing. Most likely dragging some material into the gap. If you are unlucky it will make thinks a total pain to remove if it fails.

Shear pins need to be fairly, but not too, brittle so they break cleanly under reasonably predictable loads. The half hard brass alloys can be very good for this especially as being weak enough to allow a handleable size pin to be used.

The steel pins often found on industrial lathes can be surprisingly small. My Smart & Brown 1024, a hefty 10" swing toolroom machine, uses a 3/32" (2.5 mm) pin in single shear to protect the complete drive train from headstock down. A spare pin was provided in the standard equipment so clearly its assumed to be weak enough that it will break under only moderate overload.

Obviously it handles less torque, being further up the drive train, than one in the screw itself but its food for thought.

Clive

Circlip27/01/2020 12:19:23
1012 forum posts

Since most of the "Modelling" lathes from Taiwan/China are copies of the Emco range, the one they copied must have had the original Aluminium shear pin replaced with a bit of brass. 3mm Aluminium welding rod is the often recommended replacement.

Regards Ian.

peter smith 527/01/2020 17:26:22
8 forum posts

We used 1/8th csk iron rivets on all our Bantams in school, and also Boxfords. If your machine is English and more than 25 years old it will be imperial not metric. The technician changed them every year when we serviced them after the exams.

pete

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