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Wednesday, 30 August 2017

Shortening a chainsaw bar

Shortening an 18” 3/8”pitch Huztl “Holzfforma” brand bar to 14”

Short bar on Huztl 036

Why shorten a chainsaw bar?

I like my chainsaws to have bars as short as practical. This has many advantages: a lighter unit to lift, gives the motor an easy life, less bar and chain to lubricate, more power for the teeth in the cut, quick sharpening, etc. (I go on more about the benefits of short bars in my electric chainsaw entry).
Given all this, I wanted a suitable bar for my newly assembled Huztl 036, intended for thinning and limbing small trees. In my experience, the 036 is suitable for no more than a 16” bar. It can comfortably pull 16” of 3/8” chain through lighter hardwood, but at 18” it is bogging down. When the Stihl 036 was relatively new (in the early 1990s), Stihl’s recommended bar lengths were 37cm (15”) and 40cm (16”) and I think they were right. The current Stihl catalogue shows the current version of this saw, the MS362, fitted with a 20" bar as standard. That's a toddler wearing daddy's boots...
So for my new saw, I wanted to try for 14” – a radically short bar for these days of bar length anxiety. Walking into a Stihl dealer was financially frightening, I couldn’t find a suitable bar online, and the shortest 3/8" pitch bar from Huztl was 18”. So I thought I’d try something I’ve been daydreaming about for some time: cutting a bar to a shorter length. I had a cheap 18" Holzfforma bar from Huztl, and was willing to risk it for science.

How I went about it

First step was to work out what length of chain to use, then to make the bar to fit. I looked at a 60 link chain on a 16” bar and rim sprocket:

I like Stihl’s practice of making bar lengths to fit chains with even numbers of teeth. This means that the alternating pattern of teeth continues around the whole loop. Given this, the next shorter length of chain was 4 links shorter, so I made a chain this length and tried it in place
The 56 link chain trying the bar for size
I used a genuine Stihl bar to mark out the pattern of slot and holes on the Holzfforma bar.

Using the Stihl bar to mark the slot and holes
Then I punched and drilled the bar.
Drilling the holes

cutting the slot with angle grinder with cutting disc, using a steel bar as guide
I did have an interesting challenge in this process. When centre punching one of the bar tensioner holes, there was a small bang, and I found myself with a splinter of steel surprisingly deep in my pinky finger, a punch with a flattened point and no mark left on the bar. By chance the tensioner holes aligned with spot welds from laminating the bar layers, which had left hardened patches of steel (spot welding brings spots of steel to melting temperature, and when the electrical resistance heat is suddenly stopped, the heated spots are quenched by the cold steel around, which will cause hardening in carbon steels). I first tried to deal with this by moving the hole a little, but ended up having to temper the steel with heat to make it drillable. Thus the tensioner holes are a little misaligned.
The bottom hole is right on the hard spot weld - see the failed punch mark

Cutting the slot between the holes
Filing the slot after grinding

Chamfering the hole edges

Chamfering the hole ends

Cutting the bar to length - there's no turning back now!

cutting off the corners

Grinding a curve onto the bar

Smoothing the bar shape on a linisher

Grinding the bar slot into the bar base

Chiselling a wafer of middle laminate so it can be ground away

Tempering the bar to enable drilling

Drilling the bar after tempering

Drilling the oil holes using the old bar base as template
The new bar fitted to the motor

Outcome

After all this, the bar fit on the chainsaw. I had to make some modifications to the newly ground slot at the bar base, to remove wafers of centre laminate I had missed when grinding the slot - the chain links were catching on a remnant.
The bar looks a little wider than normal at the base, but I can live with that
The saw cuts fine with the new shortened bar. It's currently only had a few minutes to test, but bar problems would normally show quickly: pinching in the groove, failing oil flow, tensioning problems etc..
The job took about an hour and was greatly extended by caution and newness. The most difficult part was grinding the chain link groove into the newly shaped bar base - it was very hard to see what I was doing.
I recall 25 or more years ago when I was doing a lot of chainsaw milling, my chainsaw shop had a machine to regrind the slot in hard nose bars. This had a grinding wheel the right thickness, held the right distance from a table, to reliably grind bar grooves. That would be very useful for this job.
If I shorten a bar again, these would be some tips to help:
  • Temper the steel at the bar base before drilling any holes
  • It would be really good to have a proper bar groove grinding setup
With these things in place, shortening bars would be relatively simple - which is good, because there are so many over-length bars around....

Update on the bar in action

So far, the bar and saw work very well. I really like the shortness and lightness.
After 3 hours of metered running hours (I've fitted an hour meter to this saw to see how long it goes), I removed and inspected the bar. In use - mostly thinning very small cypress trees in a thicket - it worked perfectly. On inspection I did find some burring of the bar rail edges at the base, on the top side, in the section where the chain meets the bar groove after going around the sprocket. 
see the burred bar edge above the tensioning hole, in the heated section
It looks like the steel I softened here with the gas torch is deforming under chain impact. 
Chainsaw bar rails are heat treated to make them harder, you can see in this photo below: 
This bar lost a patch of paint, showing the heat treatment colours along the rails, bottom side
The blueish strip along the bottom side of the bar shows that there has been some heat treatment - probably induction hardening - to make the groove rails harder and more durable. 
I'm not expecting this to be a problem, as there will be some work hardening of the steel by the chain hitting it, and there is surplus steel in this section. However it is worth keeping an eye on. 

Sunday, 21 May 2017

Baumr SX82 Review – first impressions

Model: Baumr-Ag SX82
My friend Alan asked me to have a look at his new Baumr chainsaw. It’s the 82cc saw, which cost him just over $200, delivered. Before even starting it, Alan made some modifications as suggested by Scott O’Malley on youtube, replacing fuel lines and chain adjusting system which are known problems. 
So far, it has done an hour or so of work, working really well apparently. 
Here are the new fuel lines.

these are some of the replaced fuel lines
Here’s the chain adjuster. The original bevel gear adjuster clearly had soft teeth and appears to have burred over almost on first use.
damaged spiral gear on the chain tensioner
Modified adjusting screw on chain tensioner
He also replaced the decompression valve, after early failure.
replaced decompression valve

Obvious issues

- Plastic cover melted by muffler

- Very weak bumper spike/dog, only on left side of bar. No spike mount provided on the clutch cover, but it could probably be improvised.


The saw would probably crosscut vertically down fine, but it wouldn’t be much fun to use in felling where you depend on the spikes more. Freehand ripping (e.g. cutting logs lengthways into beams) often depends on good spikes, so I wouldn't try it unless I'd installed better spikes. 

Chain and bar

The design of the chain bar is very similar to a 3/8” Stihl bar, with tensioner and oil feed holes in about the same places, but has narrower slot for bar studs.
Baumr bar on studs

Baumr bar on left, Stihl on right

Stihl bar doesn't fit - could with suitable bushes
In nearly new condition, the chain has a lot of clearance in the bar slot, with the chain able to tilt with the tooth corner in line with the bar face.
There should be daylight between straightedge and bar face



This means the chain is right on the edge of having no clearance, and the bar becoming bound in its own kerf. With a little bar slot wear, and the teeth losing set by being sharpened and shortened, the saw would cut very poorly very soon.
Normally if a bar and chain have this problem, I’ll consider hammering the bar slot to make it tighter. However in a new saw this didn’t look like a good idea. Measuring with a vernier caliper, I found the chain drive links measure at 1.4mm and the bar at 1.6mm. 


I tried a Stihl 3/8 chain of 1.6mm gauge (which interestingly measured at a shade over 1.5mm), and it fit well. I would say that the saw was delivered with the wrong gauge chain – I don’t know if they all have this problem. With a 1.6mm gauge chain, bar and chain would fit well.

It looks like they do all have this problem. On the Edisons page where the saw is sold [https://www.edisons.com.au/baumr-ag-24-e-start-pro-series-82cc-petrol-chainsaw-sx82/], the chain is specified as .058” gauge, which is just under 1.5mm - just what I found. However the spare chains they sell [https://www.edisons.com.au/baumr-ag-24-tru-sharp-3-8-pitch-chainsaw-chains/] specifically for this saw are specified as .063”, which is 1.6mm - the right gauge for the bar supplied.
1.6mm gauge chain fits snugly
After cleaning, I noticed chipping on the bar slot rails, just behind the roller nose unit. 
This is where the bar might get some hammering from a slightly loose chain. I’ve seen chipped bar rails plenty of times before, but usually only after bad burring after a lot of wear and neglect to dress the bar. Chipping on a new bar suggests a problem with heat treatment – but perhaps indicates the bar has been heat treated which is at least an attempt at good quality.
The rim sprocket was a perfect match for a standard Stihl 3/8” rim sprocket.
Baumr sprocket

Stihl sprocket

Oil pump [added 30 June 2017]

Our neighbour Shaun also bought an SX82 and gave it a first run recently. After a little cutting, Alan noticed that the chain wasn't getting oil, and there was oil running out from under the clutch cover. Dismantling revealed missing hold-down bolts for the oil pump: easily replaced and the saw back in action soon. During this exercise the clutch drum bearing was found to be totally dry - risking damage to the crankshaft. 

Conclusions

This saw is incredibly cheap. It works and seems quite powerful, but has a range of problems from new which really need to be addressed in order to use it at all. You need to be pretty handy to do all these things. The things that need attention before first use so far include:

  • replacing chain with 1.6mm gauge chain (or bar to 1.5mm) 
  • replacing fuel lines with silicone fuel hose
  • greasing clutch drum roller bearing
  • checking oil pump bolts

We’ll see how this saw lasts over time. Maybe the motor itself is fine, and the saw will become reliable after initial problems are addressed. Perhaps I’ll update this post later...

Monday, 20 March 2017

Making a Cant Hook

If you’re going to work with logs, you need a cant hook (unless they’re all too huge to move without machinery or all so small you can pick them up with one hand). Crowbars are very useful, tractors are marvellous, but for a person to be able to move logs around while cutting, milling, building, etc., a cant hook is indispensable. I first met my wife and in-laws when I visited a blacksmith to ask him to make me a cant hook, so they have a special place in my life as well.
Cant hooks allow a person to roll a log with modest effort and ample control. Along with a couple of strong crowbars, a log buggy and a few other bits and pieces, you can move logs around surprisingly effectively. Without these tools, logs are heavy, unyielding lumps that risk doing harm to your body if you try to move them at all. Don't think that you can substitute a crow bar for a cant hook: using a crow bar to roll logs is like eating spaghetti with a spoon. 
I’m very happy with the design of cant hooks I use. The hook is permanently attached to the handle and is easily swung onto the log.  Some cant hooks simply have a hook with a ring (at the handle end), and a crowbar or wooden spar must be put through the ring as the lever. This is a terrible idea if you need to roll a log more than once: you need to do a lot of bending over to pick up the hook and ring, your fingers are at risk of crushing and it's slow and awkward (I tried it early on). A hook with a ring can be useful to roll really large logs when pulled with a tractor and chain, but I have rarely needed to do this.
I use leaf spring steel for the hook, point and hinge. Spring steel makes for a much stronger hook than mild steel, thus enabling a lighter tool. It’s also usually free and being recycled. Trailer springs are often the right size of flat bar: about 44mm x 6 or 7mm. If you couldn’t get leaf spring (from the tip, or from a spring works or suspension shop bin), you might be able to flatten large coil spring or find some other high tensile steel. If not, mild steel will do - I'm sure many good cant hooks have been made from mild steel or wrought iron, preferably with steel points welded on.
10mm threaded rod is used to attach the point to the handle, and a 10mm bolt (with 2 nuts to lock together) to attach the hook to the hinge.
I harden and temper the points of the hook and point, so they stay sharp longer and are less likely to be accidentally bent.
The holes in the hook and hinge are drilled (not punched) so that there is a smoother bearing surface for the bolt. Of course you need to carefully normalise the steel before drilling, by heating to red heat and cooling slowly in the ash bucket. 
The threaded rods which hold the point to the handle are welded into punched holes in the point. I use general purpose electrodes to weld them in, and re-heat the steel in the forge immediately afterwards to normalise and avoid brittleness at the weld. 
It’s very worthwhile shaping the back end of the hook and carefully positioning the hook in the hinge, so that the hook can’t swing back and hit the handle. Your fingers will sometimes be there….
The hinge is also set so it stops the hook from hitting the point, and blunting it.

I make handles from spotted gum, which is very tough. I start with a straight-grained piece of 75 x 50 (can I say 3” x 2”?), 1400mm long, which is then sawn into a taper both ways, then planed with an electric plane into a nice round shape: first square, then octagonal, then rounded; then use a hand plane to finish. I put some red paint on the top of the handle to make it less easy to lose in the bush, and rub the handle with linseed oil (raw) to reduce checking and splintering: it mostly reduces the drying and wetting of the surface, and consequent surface splitting.
Here are some photos to give you dimensions (in millimetres) and shape:
The main dimensions and shape - it's not an exact thing. 

A bird's-eye view of a cant hook doing a shoot on a living room floor. 

This shows the hook hinged back as far as it will go. It stops before it hits your fingers.

This is the hook as far forward as it will go - missing the point. 

The bump on the point plate is where a 10mm threaded rod is welded on. The other 2 threaded rods are under the hinge.  Note the double nuts on the hinge bolt, tightened together to allow free movement of the hook. 

The 10mm threaded rods come thru to the back and have nuts and washers.