Thread: Lopro sprockets again

The use of lopro chain for milling has been raised a few times in this forum starting about 3.5 years ago,.

For those that have not heard of this chain before it is a low profile 3/8 0.050 chain and it is made for small (~50 cc) chainsaws. Apart from myself using it sporadically I don't know of anyone using this chain in a larger saw on a CSM on these forums but it is being used this was in the USA and Europe.

The pros are that it's kerf is ~15% smaller than regular 3/8 chain so there is less wood converted into sawdust which results in a smaller load on the powerhead and slightly faster cutting speed
The cons are that it needs an 0.050 groove bar and because it fits (poorly) on regular 3/8 sprockets and it stretches so much when placed under a lot of strain it will eventually jump a regular 3/8 drive sprocket when used on bigger saws.

I have been running this chain on my 441 using a conventional 3/8 050 drive sprocket, but to stop it jumping the sprocket I have been tensioning the chain extra tight and now the chain has stretched too far to continue to be used safely.

Unfortunately none of the drive sprockets made for smaller saws specifically for this chain will fit the larger drive spline on bigger saws.
By way of comparison a regular 3/8 8 pin sprocket has a diameter of 40.75 mm whereas the lopro chain needs a sprocket that is 42.45 mm.
This 1.7 mm difference is enough for a drive link from a lopro chain to eventually miss its drive slot and cause the chain to jump the sprocket.

A couple of years ago someone it the US noticed that a 404 8 pin has a diameter of 45.30 mm and turned this down on a lathe to the 42.45 mm and found it worked successfully over a long period of time.

Back in 2010 I indicated that a company in the US was making these sprockets and that they would cost $19. Well unfortunately they now cost $30 which to freight has to be added so I decided to have a crack at turning one down myself.

We all know that drive sprockets are HARD (they have to be) and I was warned by postings on the arboristsite to expect problems.

To assist with the turning I made up an arbor from a 32 mm mild steel rod and turned one end down so that it fit the 28.2 mm diam inner recess in the 404 drive sprocket. Then I drilled and tapped the end of the rod and turned up a 7 mm thick milds steep cap that firmly forced the sprocket onto the end of the arbor via an 8 mm allen bolt.

I used a carbide bit and lots of coolant. The bit had to be pushed very hard into the sprocket to get it to bite and even then only fine purple shavings came off. The biggest problem was turning the small area of the sprockets where the drive slots were the bit chattered like crazy and it broke two of the 3 carbide tips turning this area. Anyway after a fair bit of mucking about I managed to do it. My sprocket came out to be 0.15 mm undersize but it still should be OK.

Turning nearly 1.5 mm off the outside of the 404 sprocket means the area of support remaining for the drive links on one side of the sprocket looks very thin but that is on the outside and there is plenty of meat left on the inside directly under the drive links. I only plan to use this on my 441 as I think the bigger saws will stretch this chain too far in our hardwoods.

Os all up it cost me the price of a 404 drive sprocket and one TC bit (total of $12) which is quite a bit cheaper than the US product.

I was going to post some pics but they all just look like drive sprockets - I can still do this if anyone is interested.