|Forum topic by PG_Zac||posted 03-07-2009 10:53 AM||5303 views||3 times favorited||7 replies|
03-07-2009 10:53 AM
For those who have been waiting, here is the revised deign of my prototype slabbing jig posted at http://lumberjocks.com/topics/6756
There were some operational shortcomings with the original design, and I have attempted to correct the issues in this design. Note that I have not yet built & used this one. I know it will be an improvement, but I cannot say how much of an improvement, or if any new gremlins will pop up.
Firstly, definitely use a ripping chain. I used a standard chain for my first (small) log and it was quite an effort. The ripping chain chews through much easier, and is far less likely to bog down.
There are 3 significant changes:
1. The sled is wider. The reason for this is to give more bearing area when feeding into and out of the cut after the guide rail is removed. I found that I had too little sled on the cut face to give stability before the bar was in the wood.
2. There is an extra cross-member on the sled, with spare holes to let you chose its position. This is because I found that, with smaller logs, there was too little support to line up the bar parallel to the cut face. I’ll explain this later in the recommendations section below.
3. I’ve added a curved in/out feed ramp to the chain-bar clamps. This is because the square ends tend to bite into the log while you are moving the unit through. Continually dealing with that little hang-up is too distracting, and can cause a loss of cut quality.
My saw is the Stihl MS460, with a 75cm bar. More than likely it’s not the same dimensions as yours, so you will need to modify to suit.
1. Find out the internal structure of the bar from the supplier, this influences the clamping. If the bar is laminated and the centre lamination has a void to reduce weight, make sure you don’t clamp on the hollow section. If the nose has a sprocket, avoid clamping on the bar in the sprocket area.
2. Make sure that the clamp bolts are at least 10mm away from the chain teeth. Under load, the chain does not always stay tight up against the bar, and may make contact with the bolts if they are too close.
3. Make sure the bolts are no more than 15mm away from the teeth. When you tighten the bolts there is a lot of force trying to bend the clamps. The wider apart the bolts are, the easier the clamps will bend.
4. Before drilling the holes for the nose-end riser attachment to the sled, make sure you have full, unfouled travel of the sled on the machine end. I found that, in my desire to have as much cutter available as possible, I placed the riser too close to the machine and it fouled when I tried to make a deep cut. It also can affect the operation of the manual brake.
5. If you remove the bumper spikes before fitting the jig (as I have done) you need to understand that you have also removed a safety feature in the event of a chain break. I am not too concerned about that though, as the clamp bolts will do the same function as that missing safety post.
6. Do not mirror the design to make a left-hand version. The fuel tank cap needs to face up or sideways while working.
7. I haven’t figured the best / easiest way to make the clamp ramps, but my first idea is to cut away three sides of the square section, leaving a portion of the side that is facing the log. Bend that piece into a smooth ramp, and the problem should be solved. That may not be strong enough to last, so maybe I need to rivet a section of flat bar onto the square tube in a shape similar to what is shown in the model.
1. If possible, raise the log to waist high. It gets very tiring working bent over like in my pictures. Also, you want to ensure the chain doesn’t cut into the ground – Sand is BAD for the chain.
2. Do yourself a favour, and get a Heavy-Duty air filter.
3. Always wear safety gear, including chainsaw pants or chaps. Look at my pics, and you’ll see that I have contacted my legs more than once. Without the pants, I would have lost chunks of leg. I was being careful. Careful is not always enough.
3. Try to avoid cutting charred logs. The carbon mixes with the oil and makes a grinding paste which wears everything faster.
4. Always work with a sharp chain. If you are getting a fair amount of dust from the cut, the chain needs sharpening. You should be getting a lot more chips and flakes than dust.
5. I keep a spare pre-sharpened chain on hand. Sometimes I’ll swap chains and continue working, rather than stopping for a sharpening session. Learn how to sharpen correctly.
6. When you start a cut, make sure the machine-side clamp is against the log. As the chain bites into the wood, it pulls the machine hard into the log. If the bar clamp is away from the log, the sudden pull could be a problem.
7. When starting a cut without the guide rail, a sled cross member should be on the log’s cut face for stability and alignment. This is why there is an extra cross member with optional positions – the cut width determines the position of the cross member.
6. Have at least 6 wedges on hand (I prefer 8). Apply the first 2 wedges after the bar is about a foot into the cut. Another pair should go in at about halfway. The final pair just before the chain breaks through the end. Use more wedges if the chain is binding during the cut.
7. Stopping the machine during a cut for fuel or wedges is not a problem. When you restart, just back up a short way to give the chain an easy start before hitting the throttle again.
8. Understand that you are dealing with urban lumber. There is a reasonable chance that there will be nails, screws, fence wire and who knows what else embedded in the trees – possibly invisible below the surface. Either get a metal detector and check, or prepare to buy extra chains. These foreign objects could also cause a chain to break under load, so keep yourself protected as best you can, and be sharply aware of any sound changes while cutting.
9. If possible, have someone with you while you are slabbing. Their primary role should be to ensure that no people or animals get within 20 yards of you while the chain is moving. You don’t want to hurt a neighbourhood kid by accident because they were inquisitive.
10. Storage – When I have a whole log’s worth of slabs to store, I like to reassemble the log in sequence with stickers between. This way I can easily find book matches for a project, and I don’t have to try to remember which planks came from which tress. After reassembling the log, I use ratchet straps to bind it together. There are no issues with placing weights on the pile to reduce warping – each slab supports the other during drying.
-- I may be schizophrenic, but at least I have each other.