Hello, and thanks in advance for any advice.
I have a manual home built mill. It has cut pretty well lately, but I just started noticing that once I get the log cut so that it is flat on all four sides, the width of the cant may vary up to an 1/8 - 3/16 from one end to the other. This isn't a major issue for me because I am cutting the lumber for myself, but I would like to figure it out. So I may have an 8x8 cant at on end and an 8 - 3/16 x 8 - 3/16 at the other. I have cooks roller guides on the mill, and once I noticed I adjusted them again following their video. It still is off slightly (1/8"). Is there something else that could be off or happening? Or, do I just need to readjust the blade guides? I built the tool that sits on the blade in the gullet and I measure down to the bunk at both ends to adjust.
Thanks!
Have you measured from the blade down to a bunk at both ends of the mill? It should be the same measurement. Assuming it is, there are really only three things that can cause this:
1) Mill rails are bowed or are bowing as the head travels down the mill.
2) The cant is moving due to stress in the log.
3) The blade is wandering in the cut (not likely your problem).
What is your mill sitting on? Make sure it's level and solid. My fine adjustment outriggers sometimes loosen themselves off, causing accuracy issues.
My first thought was stress in the log lifting the cant off the deck. But if the problem is always at the same end of the cant, either the tail or the head, then the issue must be in the deck of the mill.
What Ga Mtn Mans says but do it with the cant on the mill .
Differences between end thickness of cants by this amount (~3/16) is common in portable milling and has to do with the flexibility of a long length of mill rails. As stated above yes it can be due to cant stress or mill problems too. It is less likely to be cant stress if you are talking about differences remaining after light cuts are taken.
If it is due to flexing of mill rails you will be able to see , by sighting along the length of a cant of a cut just made, that the cant has a slight crown or dip in it depending what is going on with the mill setup. For example if the 8" is at the front end, the 8-3/16 at the back, then shimming under the front supports so that the mill bed/rail is actually lifted by 3/16, should lead to some or all correction of the 8" (turning it in to 8-3/16).
In other words a properly setup mill cuts parallel to the bed supports, and the same distance from each bed support. If the mill bed is arched, then the saw travels in an arc too. The cut cant is stiff, like a straightedge relative to this arc, so it is cut in an arc too. 8 at one end and 8-3/16 at the other end. Sight along it and you will probably see it is not a straight line but has an arc dropping off at the smaller end.
I'm new to all of this also, but sometimes I notice that just before the blade exits the cut it is above the rollers and drops down when it exits the cut. To me this indicates that my guide rollers aren't exactly parallel to the frame, and causing the blade to "climb" as it cuts.
Good luck,
Ken
A band that jumps when it exits certainly indicates that is not cutting true. Could be alignment, lots of things. If it's a progressive thing, I.e not so much when the band is fresh and more jump after some sawing time, it's a dead sure indication of a dulling band. A perfectly sharp and perfectly aligned band exits the log with no noticeable jump, and the sawdust rooster tail is evenly balanced above and below the gullets.
could this also be a tooth set problem? are your teeth hitting your wheels?
Thanks for all the advice. I didn't have much time to mess with it yesterday, but I did measure down from the blade to each of the bunks. There was a slight difference in the measurement from one end to the other, maybe 3/32. So, I placed a thin piece of metal up under the last bunk (I'm guessing 3/32 thick). I cut the log on one side. Flipped it 180 Cut it again and the cant was still about 1/4" bigger on the end with the shim. However, the odd thing, I made several one inch passes on the cant and the width of the cant got to within about 1/8" of the same width.
Also, the boards that come off the mill I can check with a caliper and they are pretty much exactly the same thickness from one end to the other. I just can't wrap my head around it.
Quote from: Georgia088 on January 09, 2018, 12:18:56 PM
Also, the boards that come off the mill I can check with a caliper and they are pretty much exactly the same thickness from one end to the other. I just can't wrap my head around it.
That says to me that the bed is not dead flat. My mill has toe rollers that can lift either end of a log to get the pith centered. If you forget to lower the rollers after making the initial cut then you get a tapered cant, however, if you continue to saw boards from that tapered cant the boards all come out "planar" for lack of a better word - or the same thickness all the way. Of course the bottom board will be tapered as something has to make up the difference in the example I cite here - did it just last week.
What if you run two strings the length of your mill next to the cant, one string from the first bunk to the last bunk with a block under each end of the string then use a third block the same thickness (it is best to cut all the blocks from the same board) to see any changes as the saw travels down the mill and the other fastened to a stake at each end of the mill and set at the block thickness height but no blocks under the string. Then you can see if anything changes.
Another thought, sometimes the log clamp(s) can lift the cant when tightening, check under the bunk as you are clamping.
If one bunk from one end is 1/8" higher then the other end and your track is 16', the will throw things up a easy 3/16" if not more. A string level and string is your friend. That and two wood blocks. One on the first bunk and one on the last bunk.
If you want an easy way to check level anywhere on your mill, house, site, etc. get a section of 1/4" poly tubing long enough to reach where ever you need to check. Fill it with water, and attach one end to the piece you are trying to level to. Make sure you use the meniscus on the water line in the tube as the site line (top or bottom) when you attach your line. Plug both ends of the line, and move the other end of the line to the point you are trying to check. Unplug both ends of the line, the water will seek level in the line.
I learned it decades ago from a man when he set up mobile homes. I'm sure there are U tube video's on how to do it.
I shoot a line with a laser...
Seriously Kbeitz??
I honestly thought you were going to post a photo of a level systems that used the rotation of the moon and a reference point on the sun to determine level, made before 1900 out of brass, of which you have several, and all in working condition, one of which you found at the local salvage yard!!
Southside I'm pretty sure I saw some of those in the background of one of his pictures but they were proven to be inaccurate due to a miscalculation in the curvature of the earth, the flaw was only discovered after the deployment of geostationary satellites.
I use a laser.
I level mine with a transit.
This is where I would start.
Make sure your frame is rigid even when or especially when you have a log on it.
Level your track side to side and end to end.
Parallel your bunks to the blade, side to side and end to end.
This should get you cutting both parallel and flat.
You mentioned the blade dropping after the cut. Get a strong light and magnifying glass and look at the teeth. The outer tip is what keeps you cutting straight. Looking down at the point there should be no light being reflected back at you. Check that the set is the same on each side.
When you get 8 on one end and 8-3/16 on the other, raise up the mill bed at the 8" end, NOT the bunk(s), however you can do it, such as a hard shim like 1/4" plywood or hardwood, and see what happens to the thickness-of a stiff beam-at the end you raised with shims.
Your measurement of end to end variation in a stiff beam is a measurement method where you already know you can detect 3/16" variation.
Georgia088 what is your bed made out of? How thick? Dimensions?