How to make one of these (hardened steel lever)

The part in the picture is a pivoted lever that carries the blade guide roller on a Bosch (Scintilla) Jigsaw. I have had numerous attempts to buy the correct spare part but the jigsaw is now 'vintage' and this part is no longer available.

The material is 2.5mm thick steel that has been hardened and is 12mm wide at the break. A file just skids over the surface and I would describe it as glass hard. I do not have heat treatment kit or the experience/confidence to go to the trouble of copying the part and then risk breaking it the first time I use the jigsaw!

I hate throwing things away especially a quality tool and without doubt is the best tool purchase I have ever made. Bought over 40 years ago as it had the then fairly innovative, 'pendulum' action, it has renovated five houses and cut everything from 6mm steel plate to tree roots. It has had one set of brushes and the only other repair is to shorten the mains lead when it fatigues at the cable entry.

If I was going to make one I think I would mill it from the solid (EN24?) but I would still have the hardening problem.

What would you do?

Ian P

Edited By Ian Phillips on 03/08/2016 21:06:48

I'd try and find a piece of A2 air hardening tool steel to make a new one. Get it from a metal supplier and ask for certs for your piece of A2. Make smooth radii and fillets at all changes of section, smooth finish (unlike your mass production Bosch stamped part with rough punched holes and huge bend tool marks). Google heat treat for your brand of A2 (very simple propane torch heat to red heat / air cool / repeat / air cool temper usually in A2, for this size of part) and follow to the letter. No water or oil quench needed. Result will be very strong very hard new part. JD

Jeff

Admittedly I have not done a search yet but I cannot recall any of the usual MEW suppliers having A2 steel in their catalogues. I can imagine getting a piece 2.5mm thick 60mm square and with any details of provenance might not be easy or cheap.

Other than that I quite like the idea of making it myself.

Ian P

Bronze braze? Have someone TIG weld it? You might be able to bend a new one up from sheet. It depends how much more work you anticipate doing with the tool.

A2 will likely be available at toolmaking suppliers or metal supermarket if there is one near you.

It will likely be at suppliers in bar form rather than sheet. I visualized making it out of a block rather than bending up a sheet.

Bosch likely made the original out of austempered AISI 1060 or 1080 steel, bent in the soft state then austempered. I designed and made many parts like it for the valve industry and for office equipment parts. Austempering requires a good proper heat treat chain belt furnace and careful heat and time controls, not simple in home shops but widely available at commercial spring makers and 4 slide shops.

Bending heavy sheet to tight shapes as part in your photos usually requires some bend/form tooling and significant press tonnage. If A2 could be found in sheet form it will require much more tonnage to bend than 1060 or 1080 in soft state. Can be done of course but likely much easier to carve your item from solid A2 and air harden. No bend/form tooling, no tonnage required, and heat treat usually dead simple. JD

Ian,

It doesn't help much regarding making the replacement ['though I think your original plan is sound], but I would just mention that the original part has obviously been hardened to the point that it is brittle. Excellent as those jigsaws are, I think this may be a manufacturing fault and I would aim for something tougher.

MichaelG.

like A2 tool steel?

I'd a think about why the piece is hardened. It could be that the design calls for a hardened steel pivot to rotate in a hardened hole. It would then seem to be unlikely that the whole piece needs to be hardened but that was the most efficient production option. An alternative would be to make the piece from an un-hardened steel and insert bronze bushes for the pivot holes.

HTH,

Rod

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Yes ... In deference to your expert advice, I was not discussing material; merely commenting on the obvious over-hardening of the original component, and suggesting that a tougher condition would be better.

MichaelG.

I disagree that the part was too hard when it was manufactured. It has survived millions of operating cycles over 40 years without failing. Because its tough (read hard and rigid) it would not have flexed very much, but millions of 'not very much' have eventually culminated in its fatigue.

Ian P

Looks like a simple blacksmithing job to me. I would think any half-decent agricultural engineer could soon make up a replacement, properly hardened . . . if they can't repair the original. If it's done 40 years it can't have been all that badly made!

If it was mine, I'd try cutting and hot bending one from any old bit of steel plate. It might not last another 40 years but I might not care by then.

Have a close look at where it fits and see if a bigger bit of something less strong can fit. What was appropriate for mass production may not be the only solution.

I did think of milling the part from solid as Jeff states, bending that part would require making tooling so not really applicable to a one-off.

Bosch seem to have made numerous developments and versions of this jigsaw, looking at online part catalogue images I can see identical 'looking' parts but they would have to be ordered and purchased to see if they would fit.

The easiest thing might be look out for someone selling the same jigsaw for 'spares or repair' and hope its not the same part thats broken!

Ian P

Not sure why it would need to be through hardened? I'd make it from low carbon sheet steel by cutting, drilling and folding. In a perfect world I'd case harden it.

Andrew

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That is your prerogative, Ian ... But it seems obvious, even at this distance, that it has suffered a brittle fracture, rather than a fatigue failure.

That said; I will stop interfering.

MichaelG.

Hard to know if it would be possible without seeing the whole machine but as the fracture is obviously the weakest point I would try to incorporate a triangular gusset in either side to reinforce that area and help resist the bending force at the point of the fixing hole.

Take a sheet of paper and wrap it around the two 'flaps'...mark outline and holes with fine pen being sure to prevent any slipage........mark in the broken base parts as one outline (obviously) Transfer the 'drawing' to guage plate and mark out carefully using carbon paper or similar...or transfer to thin card and cut out an accurate template then draw around onto guage plate. Cut pieces or scrap sheet for 'sandwich' exactly 12mm thick and set aside. Drill and clean all holes THEN cut out part from guage plate. Heat with blow torch/bricks until bright red.....place against scrap sandwich, fit in vice and fold ONE of the flaps up only. Take second heat and place scrap against bottom of part,...fit into vice and fold other flap down.....

.........Check of fit and accuracy on jigsaw.

Heat to red heat and drop into one pint engine oil (preferably non synthetic)........remove part and clean with wire wool,.........place on piece of sheet steel and heat from underneath the sheet with blow torch (or over forge) ....keep the part moving with pliers until it is uniformly 'straw' colour.........drop back in oil.......clean and fit.

The only thing I would add to Bob's suggestion is that I'd drill the holes after bending (but before hardening) to be sure they align perfectly. I've seldom managed to bend anything accurately enough to ensure precise alignment of holes that were pre-drilled like that. I know my limitations

2 cents

You can heat up small pieces of steel with a cheap welding kit.

zap the piece while its over a jug of dirty engine oil and tip the red hot piece in

retrieve with a magnet, clean it up and grind away the welding part

I'd just make one up out of flat steel plate, or even flat bar bent and welded. It just holds the guide roller so no need to be hardened. Mild steel will probably last well enough for home hobby use. Or pick up another jig saw at a boot sale for $5.