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Member postings for jaCK Hobson

Here is a list of all the postings jaCK Hobson has made in our forums. Click on a thread name to jump to the thread.

Thread: How badly do I need a surface plate?
22/07/2019 08:32:57

My cheapo granite surface plate is a lot flatter than my granite worksurfaces or granite tiles. My conclusion comes from the close surface effects of sticky/floating you get between two 'flat' surfaces.

Thread: Building a Belt grinder - advice please.
26/04/2019 18:31:02

The high power knife grinders can be reasonably dangerous but I guess losing whole fingers is less likely than a lathe. I've trapped a finger, ground the odd knuckle, and a common reported issue is a snapped belt slapping you in the face (never happend to me). Guarding is sensible but hugely impacts flexibility of the tool when using the slack portion of the belt. The Goset grinders like I linked to in my first post now have much better guarding with CE approval but they cost more. I really like them - well made, good design, and you get a lot for your money.

I would think you can at least half the power if you are using it for wood - the limit on belt grinding wood seems to be the heat generated which burns the wood. The big power is only required for rough shaping metal on coarse grit - if you are just finishing up a mitre on a 2x4 then you will not be needing anything like 1HP per inch!

25/04/2019 16:55:33

1HP per inch of belt is accepted wisdom for knife grinders if you are going to do a lot of grinding. I know people who have more HP but they make a living from grinding. I have a Goset grinder which is 1.1KW for 2" which is fine for me I have used 1hp for 2" and it wasn't always quite enough. (I have a home build 2HP 2", and an under-powered 1HP 4" which both get some use, and a couple of the DIY store 4" (one converted to use 2" belts) which just gather dust).

If I was making a grinder, I would go for 2HP and stick with 2" for knife making. You don't tend to use the whole 4" width evenly when grinding bevels and you don't often need to flatten stock much wider than 2". 4" belts are more expensive. You go through a lot of belts. Longer the better- as they will run slightly less hot and will be cheaper per inch of belt (you pay for the joins).

I'd even consider using narrower belts.

Thread: Any Recent Progress in Induction Heating ?
27/03/2019 07:54:46

I'd be really excited if someone comes up with a reliable, cheap soluition. I tried and failed. Very fragile - read down the tutorial and it hints that if your power supply isn't right then it self destructs. i've destroyed one big one and two small ones being slightly careless with the sequences of start-up. Banggood now do one twice the power if you can arrange a suitable DC supply.

Or you can buy a proper one for blacksmith forging for about £5K (all protection circits and stuff to auto adjust according to load 'built in' ) - I have limited experience forging a knife and it left me with the conclusion that you will need to adjust what you think you know as my knife was riddled with stress fractures probably from forging too cold.


Edited By jaCK Hobson on 27/03/2019 07:55:34

Thread: Heat hardening?
22/03/2019 08:54:52
Posted by Steve Crow on 21/03/2019 17:12:26:

a brass one would double up as a blueing tray for brass chips.

I'm confident you could use a copper one for blueing.

20/03/2019 18:13:33

Copper has the best thermal conductivity so better for even heat. I think you could get acceptable results with other materials. Dimensional stability during quench could help.

Steffen Pahlow seems to use sandwich of steel parts held together with binding wire. just wraps in binding wire - I would be surprised if the dimensional stability of the wire contributed to reducing warping. Daniels uses binding wire approach for other things - helps retain heat for really small items like pivots and holds borax to reduce scale.


Edited By jaCK Hobson on 20/03/2019 18:19:55

Thread: Hardened Silver Steel Shattered - How to Avoid?
15/03/2019 08:17:47

Posted by SillyOldDuffer on 14/03/2019 20:42:14:

tempered with a blow-lamp instead of the oven.


My guess would be that the blow lamp got it hotter than the oven. Oxidising colours are a poor judge of absolute temp. They can be reliable for indicating relative temps if all conditions are the same - same material, same heat source, same atmosphere, same surface preparation. I think you have done a perfect demonstration of this - it looks like both success and fail are 'dark straw' but seem to behave differently.

15/03/2019 08:10:39
Posted by Neil Lickfold on 14/03/2019 18:40:01:

There is W1 and O1 in the silver steel range.

I would agree that 'silver steel' may cover a broad range of alloys but the composition of modern silver steel should be better understood and should not include W1 or O1.

W1 is good for small edged tools, Not that easy to get hold of in UK in small quantities. Easy to heat treat and anneal. Very fine grained. Old files are often similar alloy.

O1 easy to heat treat, not so easy to anneal. Can get it hard for larger sections than W1. Fine grain. Ground flat stock is often O1. 'Shim steel' may also be ground flat stock and can often be something with less carbon and won't get as hard.

Bright round bar in small diameters is often silver steel. I think 'pivot steel' is similar, if not silver steel. I wonder if., as silver steel is usually round bar, it is expected it might be turned in a lathe, and therefore has the composition been designed to give larger grain in order to make it easier to machine on a lathe.? That question obviously exceeds my knowledge of metallurgy but would be easy to answer for someone who knows.

Edited By jaCK Hobson on 15/03/2019 08:19:30

14/03/2019 18:07:51

The grain in the out of focus failure doesn't look that bad for silver steel but difficult to tell. If it is bad, then overheating would be the most likely cause. Use a magnet. For small silver steel like this, you don't need to soak for very long at all.

You need to cool to room temp before temper. Some steels, stainless in particular, need super cooling to get full hardness (liquid nitrogen). For silver steel, it doesn't really make much difference if you delay between quench and temper. (You should do super-cooling as soon as possible after quench).

If using a domestic oven then I would have thought that a single temper for one hour at 220C should do. However, the fail shows that the temper wasn't good enough. You could increase the temp a bit - especially if just cutting brass. So maybe 240. Some steels do need multiple tempers to get the best, but not silver steel.

Do you know if you did anything different for the successful version - maybe tempered for longer?

You can keep increasing temper temp without re-hardening but if you over temper then you will have to re-harden. You can repeat the cycle a lot - the risks are stress cracking or carbon depletion.


Edited By jaCK Hobson on 14/03/2019 18:11:55

09/03/2019 10:08:23

For the current application I think the tool would be fine if you just added a tempering cycle at 220C as suggested.

A few guidelines for next time:

You need to heat until the steel is non-magnetic at least - that is easy and reliable to check. "'red' heat looks different depending on how bright your surroundings are.

Speed of cooling also depends on size of part - bigger parts may well need brine and agitation. A watch pivot would probably be hard in air cooling.

Toughness depends on grain size in the material. You can manipulate with heat treatment. Heating too high and too long will increase grain size. Repeating treatments just above critical / non magnetic will decrease grain size. Fine grain is much better for toughness. Big grain makes it a bit easier to harden. My experience with silver steel is that it is difficult to get really fine grain (compared with O1) - I speculate that this may be intentional to help machining?

You can get a soft skin on heat treated material due to carbon depletion - an initial file test can fool you - sometimes you will find it is hard under the skin. More likely to happen if part was heated high for a long time (as could happen if you forged something or in initially creating the raw stock).

Thread: What MIG Welder should I get?
17/12/2018 12:36:26

If you are going to get a cheap Mig, get the Clarke. With Mig, the wire-feed is critical and the Clarke one works OK which is largely why they get recommended. Also, if you have machine mart near you then you can pop in and get all the spares. If you want easy welds, get proper welding gas (argon/CO2 mix) and make sure to prepare the weld properly - super clean.

But, your stick welder is probably going to give better penetration on thick steel - ie. stronger welds. And it isn't nearly as fussy about cleanliness of the material. If you can't get good results, check your power supply - if you are a long way from the house then you may be getting voltage drops.

Mig has real advantage for thin material like car body panels.

Tig requires another level of preparation and cleanliness.

I'm just hobby and own the cheapest stick and cheapest Clarke Mig you can get, but that means I'm familiar with the end of the market you are considering. Both of mine are probably 10+ year old and going fine.

I think that, at least at one time in history, the Clake Mig welders were made in Italy.

Edited By jaCK Hobson on 17/12/2018 12:47:00

Thread: Dangerous Ultrasonic Cleaner Electrical Failure
27/07/2018 16:03:40

I have been a fan of cheap goods from Ebay and BangGood but some recent experience have made me wonder...

I bought one of the cheap blue demagentisers with the little red button. It really works but I left it under a notebook (heavy enough to activate the red button) for 5 minutes. It melted.

I bought a thermostatially controlled soldering iron which heats to 450C in 40 seconds... and left it on for 8 hours. It melted.

Luckily the melted plastic in these products has a very pungent smell.

I'm not completely put off but I would strongly advise that these bargains are only operated under supervision.

Thread: drilling files
19/07/2018 19:12:41

I would love to be able to drill files but, after many, many attempts, my conclusion is that the best approach is to temper or anneal. I can't do the carbide approach and I don't think it is reliable enough to try on something you may have invested hours into. To temper, heat to black heat or at least stop as soon as you see any dull glow. You _should_ be able to drill after that. Finish the blade quite well with maybe .5 or 1 mm edge thickness. Harden and temper.

Good files are easy to heat treat to reasonable performance. You need very little soak time. Heating till non-magnetic and quenching in water should do it. Temper in oven for one hour at 180c - if still too brittle, do it again slightly hotter say 200.

Then grind to finish - but don't let it get hotter than the tempering temperature.

Thread: Warco WM250 Lathe and Warco WM18 Milling machine (Advice please)
27/04/2018 08:02:03

Isn't there any way to adjust the WM18 so you can get the quill perpendicular? Shims under the front of the column? Seem odd this can't be adjusted out.

Would you expect to be able to adjust the z height of the head during milling operations without having to re-register x-y? If not, how important is it that the quill is in line with the column, so long as the quill is perpendicular?

I don't know none of this. I don't have a mill I was dreaming of a WM18 though after I saw the size of it at Warco's last open day.

Thread: It's About Time - all things horology 14th Apr 2018 Juntion 6 M25
10/04/2018 07:56:21

Reminder: This is next Sat, 10am. I promise a good couple hours of engaging conversation if you want it, or a good hog roast bun if you don't.

Thread: Castable refractory - any experiences with Ciment Fondu?
29/03/2018 08:31:33
Posted by Robin Graham on 28/03/2018 22:59:38:

The thing is going to be a bit bigger than Mike's furnace - the outer case is one of those garden incinerator bins -

Mixing the stuff is a bit of a bother. First you have to get the cat litter turned into clay. I did a bucket at a time and used a paster/big paint mixer on a big (cheap) sds drill with all the final amount of water (takes experimenting) . Then mixed with cement in a wheel barrow and a hoe, then perlite. Easier to do small batches than one big batch.

27/03/2018 16:56:27
Posted by Robin Graham on 26/03/2018 20:58:22:

A couple of replies referred to the 'right' or 'proper' stuff without saying what that actually is - like IanT I'd be interested to know!

Put 'Castable refractory' into google and it is easy to find a choice of readymixed products with different temp ratings although you get quite a bit of noise about pizza ovens.

Trouble is, there is often a min £50 delivery charge for a pallet, and you have to be available when it is delivered.

26/03/2018 16:24:46

I think fresh vermiculite works OK and also think damp was the stated reason not to use it. I made some with perlite and melted it at sustained steel welding temps and it will dissolve quickly if you use borax flux. OK for forging temps or melting aluminium. Probably not going to support making crucible steel or cast iron. I use the proper stuff now - postage is the killer cost

Thread: Why Brass??
26/03/2018 08:35:28
Posted by John Haine on 24/03/2018 17:35:11:

I've often thought that it's odd that clock wheels have symmetrical teeth - it's not as if they go in reverse is it? There's probably a better tooth form if you remove that constraint.

A justification for the superiority of the dead beat escapement is that it doesn't drive the train in reverse. Other escapements do. Harrison argued that cycloidal gears driven in reverse gave very different resistance compared to driven forward - the screwdriver argument in the link (but nothing to do with coefficient of friction, just levers). Harrison used lantern pinions because they don't exhibit this difference (and the grasshopper isn't dead beat).

Thread: Workshop belt grinder/linisher/sander
24/03/2018 09:44:54

Some nice details there and a few things I bet you will tweak. It looks like your tracking wheel or the tool arm are designed to be adjustable to take up slack - just increase this adjustment provision so you can take 90 in belts. It is really handy being able to take different belts as it gives you more options for buying bargains. However, belts are not all the same and it is worth getting quality. I find the joint is one of the most important features (so it doesn't bump when grinding0 and making good joints in cut down belts may be an art of its own.

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