Hello to all,
This post is regarding a problem I found on my BT 3000 involving a machining error on the main table.
But first-
Background:
I had a project that required some 45 degree blade tilt cuts in some 3/4 x 3 1/2" stock.
As the blade was about 2/3 through the cut it would slow down and labor through the rest of the material.
I had just aligned everything and so was perplexed at why I was having this problem. I rechecked the blade runout, the alignment of the fence and the SMT. Everything checked out fine. ( I normally try to get every thing within ~ .002" with the fence a little open at the rear.) I was using a spacer block to set the work length before the cut so there could be no binding of the part and the fence. Besides it is the safe way to cut with a right tilting blade.
Problem found:
One thing I had not paid much attention to in aligning the saw was the top of the accessory table relative to the main table. (Now my set up was the SMT on the left and accessory table on the right). But I knew this was where the problem had to be. Sure enough a straight edge showed the accessory table was lower than the main table, more importantly, it was canted down to the right!
I got out an indicator and surface gage and started to find out more and to document what I found. It wasn't good! After making sure the main table top was reasonably flat ( straight edges and sweeping with a indicator) I trammed the top of the accessory table and found it was running down hill to the right about .015" tir. I then swapped it out for another that I had and found a similar discrepancy. Moreover the top of the accessory table was about .020" below the main table at the adjoining edge. The two accessory tables were of different heights but the downhill error was about the same for each.
So far all the reading had been on the front of the tables. I then checked the reading at the rear of the tables and found they were much better especially when the accessory table was unlocked and allowed to rest with both lugs on the rear rail slot.*
I then removed the accessory table and the SMT and, reaching as far as I could with the indicator setup, trammed the top of the front rail. It was out by about .035" in 18". The right side was low. I checked the rear rail and it was only out .004" in the same distance. The rear was certainly close enough.*
At this point it was clear that I had a bad rail or something was wrong with the locating surfaces for the rail or perhaps both. To find out, I swapped out the front rail ( I have 3) the readings were very much the same as the first rail. So much for the rail, unless I was lucky or unlucky enough to have two bad ones. So I removed the rail and setup to measure the rail mounting bosses on the front of the main table. There are two front locators ( bosses if you will) one on the right and another on the left. The rail clamp screw holes are in the center of each boss. Each boss has an upper and lower locating surface which protrudes out from a finished pad. A slot on the back of the rail then rides on the upper locating surface of each boss to correctly position the rail. The rear of the main table is simarly equipped to mount the rear rail. I checked the play between the slot in the rail and the bosses to see if perhaps the rail was mis-clamped but with only about .005" clearance it was not possible to misalign the rail to the extent that I had measured. So the problem had to be in th bosses them selves.
I measured the top of each boss to the top of the main table and found that indeed the bosses were not the same the right one measured approximately .022" lower than the left. The question was which was the correct or were they both off? To find out, I mounted the rail using only the left boss to establish the vertical position of the rail and then adjusted and trammed it until I got it parallel. Then using the accessory table, I measured the top of the main table relative to the accessory table and found that they were very close to the same height. This meant that the left boss was the problem and sure enough, after repeating the rail mounting on the left boss, it was easy to see that the right boss was off location. One final check would reveal if the two front bosses were machined on a slant or was the right boss alone machined in error. I put a straight edge on top the left boss and slid it to the right maintaining full contact as I moved it. It slid right over the top of the left boss revealing a gap of about .025". This was a little more than I expected but showed that the left boss was machined in good form while something caused the right boss to be machined out of line with the left. Please note that the distance between the top surface of the boss and the bottom surface was the same, about .879" on all the bosses front rear, right and left. This meant that, most likely the entire top was refixtured between the machining of the left and right bosses, since most likely, the top and bottom surfaces of the front and rear bosses would have been done in one fixturing. I'm guessing this main table was removed from the milling machine or cnc before the right boss surfaces were machined and, when the error was noticed refixtured and the right boss surfaces machined by themselves thus causing the error. Having spent fifty years designing and manufacturing machine tools, that's my story and I'm sticking to it.
Problem fixed:
Now the question is, how to fix the error.
Option 1- replace the main table with a new one. This would of course mean finding a new or used one and inspecting it to make sure it was error free before changing the old one out.*
Option 2- repair the current one by, perhaps building up the upper surface with weld and remachining the top and bottom of the right boss to the correct dimension and location relative to the top of the table. I don't have this capability anymore but a friend up North has a machine shop so this could be done.*
Option 3- *in-situ repair; build up the top surface and remove material from the bottom surface of the right hand bossto correct the problem.
I chose Option -3 because, A- I'm cheap and B- it meant not having to disassemble and reassemble the saw. I have a serious health issue and can only spend short periods of time working on projects, Option- 3 it was.*
Did I mention that I'm cheap?
To effect the repair, I waxed and lightly greased the straight edge used earlier to determine the right boss was in error. I clamped this to the left boss with one end in full contact with the top surface of the left boss and the othe end hovering over the the top surface of the right boss. I secured the right end of the straight edge with painters tape and masked off everything except the gap between the bottom of the straight edge and the top of the boss. I filled this gap with metal filled epoxy and allowed it to cure for more than 24 hrs. I then removed the tape and straight edge and tidied up the patch with a razor and file. Carefully removing only the overfill. I then used packing tape to mask the face of a new mill file I had so that I could use it's edge to remove material from the bottom of the boss without removing any from the back face. I carefully worked the bottom surface until the rail fit onto the boss with a slight interference fit. I then mounted the rail and trammed it using the original 18" span setup I used when I was trying to determine the initial problem. Tramming the rail was actually easier than setting up and measuring the tops of the two bosses and since it was the rail that I wanted parallel anyway, this approach saved some time. Anyway the result showed that the rail was now higher on the right than the left. Just the opposite of the original problem but considerably less. I removed the rail and took *a few thousands off the epoxy on the top of the boss using the file and replaced the rail. This time tramming showed the rail was almost perfect. This worked well as the original clearance of the slot to boss was about .005" and my fix ended up with about a thousandth more than that.
I also want to mention that another factor in choosing Option- 3 was that I do not move the rails on my saw once they are set because I have a wide table on the right ( which has it's own legs and places no load or stresses on the saw rails once it is attached. Thank you) and have limited room in my shop so once they are positioned, they stay. I would not recommend this fix for those who do reposition the fence rails as the epoxy, while having good yield strength, may not wear as well as the original aluminum. Otherwise, I would probalbly have chosen Option- 2.
The final checks were made and everything checked out well. The only thing I found off was that the top of SMT is a little higher than I would like but it also flexes down to about level when a feeding force is applied to it. So for now I'm living with it. The 45 degree blade tilt cuts that originally presented a problem are as free cutting now as any 90 degree cut. So I think the problem has been sucessfully resolved.
As you can tell from the length of this post and the steps involved, it was not a quick fix although, that said it wasn't particularly difficult either. I hope this information has or will be helpful to any of you that are unlucky enough to have a similar problem although I hope that will not be the case. The unlucky part that is.
I know that I was a bit wordy but wanted to make the entire process as clear as possible. I hope I was, at least partially successful. Otherwise, for the wordiness, I apologize.
Whew!*
Regards to all that made it this far!
This post is regarding a problem I found on my BT 3000 involving a machining error on the main table.
But first-
Background:
I had a project that required some 45 degree blade tilt cuts in some 3/4 x 3 1/2" stock.
As the blade was about 2/3 through the cut it would slow down and labor through the rest of the material.
I had just aligned everything and so was perplexed at why I was having this problem. I rechecked the blade runout, the alignment of the fence and the SMT. Everything checked out fine. ( I normally try to get every thing within ~ .002" with the fence a little open at the rear.) I was using a spacer block to set the work length before the cut so there could be no binding of the part and the fence. Besides it is the safe way to cut with a right tilting blade.
Problem found:
One thing I had not paid much attention to in aligning the saw was the top of the accessory table relative to the main table. (Now my set up was the SMT on the left and accessory table on the right). But I knew this was where the problem had to be. Sure enough a straight edge showed the accessory table was lower than the main table, more importantly, it was canted down to the right!
I got out an indicator and surface gage and started to find out more and to document what I found. It wasn't good! After making sure the main table top was reasonably flat ( straight edges and sweeping with a indicator) I trammed the top of the accessory table and found it was running down hill to the right about .015" tir. I then swapped it out for another that I had and found a similar discrepancy. Moreover the top of the accessory table was about .020" below the main table at the adjoining edge. The two accessory tables were of different heights but the downhill error was about the same for each.
So far all the reading had been on the front of the tables. I then checked the reading at the rear of the tables and found they were much better especially when the accessory table was unlocked and allowed to rest with both lugs on the rear rail slot.*
I then removed the accessory table and the SMT and, reaching as far as I could with the indicator setup, trammed the top of the front rail. It was out by about .035" in 18". The right side was low. I checked the rear rail and it was only out .004" in the same distance. The rear was certainly close enough.*
At this point it was clear that I had a bad rail or something was wrong with the locating surfaces for the rail or perhaps both. To find out, I swapped out the front rail ( I have 3) the readings were very much the same as the first rail. So much for the rail, unless I was lucky or unlucky enough to have two bad ones. So I removed the rail and setup to measure the rail mounting bosses on the front of the main table. There are two front locators ( bosses if you will) one on the right and another on the left. The rail clamp screw holes are in the center of each boss. Each boss has an upper and lower locating surface which protrudes out from a finished pad. A slot on the back of the rail then rides on the upper locating surface of each boss to correctly position the rail. The rear of the main table is simarly equipped to mount the rear rail. I checked the play between the slot in the rail and the bosses to see if perhaps the rail was mis-clamped but with only about .005" clearance it was not possible to misalign the rail to the extent that I had measured. So the problem had to be in th bosses them selves.
I measured the top of each boss to the top of the main table and found that indeed the bosses were not the same the right one measured approximately .022" lower than the left. The question was which was the correct or were they both off? To find out, I mounted the rail using only the left boss to establish the vertical position of the rail and then adjusted and trammed it until I got it parallel. Then using the accessory table, I measured the top of the main table relative to the accessory table and found that they were very close to the same height. This meant that the left boss was the problem and sure enough, after repeating the rail mounting on the left boss, it was easy to see that the right boss was off location. One final check would reveal if the two front bosses were machined on a slant or was the right boss alone machined in error. I put a straight edge on top the left boss and slid it to the right maintaining full contact as I moved it. It slid right over the top of the left boss revealing a gap of about .025". This was a little more than I expected but showed that the left boss was machined in good form while something caused the right boss to be machined out of line with the left. Please note that the distance between the top surface of the boss and the bottom surface was the same, about .879" on all the bosses front rear, right and left. This meant that, most likely the entire top was refixtured between the machining of the left and right bosses, since most likely, the top and bottom surfaces of the front and rear bosses would have been done in one fixturing. I'm guessing this main table was removed from the milling machine or cnc before the right boss surfaces were machined and, when the error was noticed refixtured and the right boss surfaces machined by themselves thus causing the error. Having spent fifty years designing and manufacturing machine tools, that's my story and I'm sticking to it.
Problem fixed:
Now the question is, how to fix the error.
Option 1- replace the main table with a new one. This would of course mean finding a new or used one and inspecting it to make sure it was error free before changing the old one out.*
Option 2- repair the current one by, perhaps building up the upper surface with weld and remachining the top and bottom of the right boss to the correct dimension and location relative to the top of the table. I don't have this capability anymore but a friend up North has a machine shop so this could be done.*
Option 3- *in-situ repair; build up the top surface and remove material from the bottom surface of the right hand bossto correct the problem.
I chose Option -3 because, A- I'm cheap and B- it meant not having to disassemble and reassemble the saw. I have a serious health issue and can only spend short periods of time working on projects, Option- 3 it was.*
Did I mention that I'm cheap?
To effect the repair, I waxed and lightly greased the straight edge used earlier to determine the right boss was in error. I clamped this to the left boss with one end in full contact with the top surface of the left boss and the othe end hovering over the the top surface of the right boss. I secured the right end of the straight edge with painters tape and masked off everything except the gap between the bottom of the straight edge and the top of the boss. I filled this gap with metal filled epoxy and allowed it to cure for more than 24 hrs. I then removed the tape and straight edge and tidied up the patch with a razor and file. Carefully removing only the overfill. I then used packing tape to mask the face of a new mill file I had so that I could use it's edge to remove material from the bottom of the boss without removing any from the back face. I carefully worked the bottom surface until the rail fit onto the boss with a slight interference fit. I then mounted the rail and trammed it using the original 18" span setup I used when I was trying to determine the initial problem. Tramming the rail was actually easier than setting up and measuring the tops of the two bosses and since it was the rail that I wanted parallel anyway, this approach saved some time. Anyway the result showed that the rail was now higher on the right than the left. Just the opposite of the original problem but considerably less. I removed the rail and took *a few thousands off the epoxy on the top of the boss using the file and replaced the rail. This time tramming showed the rail was almost perfect. This worked well as the original clearance of the slot to boss was about .005" and my fix ended up with about a thousandth more than that.
I also want to mention that another factor in choosing Option- 3 was that I do not move the rails on my saw once they are set because I have a wide table on the right ( which has it's own legs and places no load or stresses on the saw rails once it is attached. Thank you) and have limited room in my shop so once they are positioned, they stay. I would not recommend this fix for those who do reposition the fence rails as the epoxy, while having good yield strength, may not wear as well as the original aluminum. Otherwise, I would probalbly have chosen Option- 2.
The final checks were made and everything checked out well. The only thing I found off was that the top of SMT is a little higher than I would like but it also flexes down to about level when a feeding force is applied to it. So for now I'm living with it. The 45 degree blade tilt cuts that originally presented a problem are as free cutting now as any 90 degree cut. So I think the problem has been sucessfully resolved.
As you can tell from the length of this post and the steps involved, it was not a quick fix although, that said it wasn't particularly difficult either. I hope this information has or will be helpful to any of you that are unlucky enough to have a similar problem although I hope that will not be the case. The unlucky part that is.
I know that I was a bit wordy but wanted to make the entire process as clear as possible. I hope I was, at least partially successful. Otherwise, for the wordiness, I apologize.
Whew!*
Regards to all that made it this far!
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