Hold a gear for cutting?

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Gordon

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I just stripped a gear on an engine and now I have to make a new gear. The first gear was brass and obviously was not strong enough. I am making a new one out of steel. I just purchased a set of divider plates for my rotary table so that I could cut gears. This is great, now I get to play with my new toys. The gear is 2 1/2 OD with a hub and 3/8 bore. I am just about done with machining the blank and I started thinking about how I was going to hold the blank on the rotary table. In the past I have used my spin indexer which uses a 5C collet so as long as I left a hub which would fit in the collet or had a bore which I could adapt to the collet I could hold on to the blank. I have a 6" rotary table and have a 6" three jaw chuck mounted to the table. Unfortunately if I hold the blank in the chuck the cutter hits the chuck. I also have a 4" chuck which I could mount to the table but even that will not clear the cutter. Any ideas on how to hold this blank? How have others done this? The only thing I can come up with is to hold my hex 5C collet block in the three jaw chuck.
 

Brian Rupnow

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Turn a round piece of steel, about 1 1/2" diameter x 4" long. Put a reduced end on it to fit into the gear, but about 1/16" shorter than the length of the gear hub. Drill and tap the end of the steel for a 5/16" or a 3/8" thread. Mount the gear on the end, put a bolt in the end of the shaft and cinch it up tight. Now, hold the opposite end in the chuck. That way the gear will be far enough away from the chuck that the cutters won't touch the chuck jaws.
 

Gordon

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That is pretty similar to what I have done with the 5C collet in the spin indexer. The problem with this gear is that it is the timing gear on the cam shaft so it only has 3/8 bore with 2 1/2 dia so I am not sure that the bore will take the torque. At this point I am using the 5C hex collet block so that I can hold it by the 1" dia hub. Looks like it will work if I take it easy but the gear is a long way away from the table.

I obviously have something more to learn because the turn table is not turning with the crank.

At this point I have had enough for this week so I am gong to go into the house and take tomorrow off. My wife is helping my daughter in Cincinnati and I have to do some laundry and wash dishes and clean the house before she comes back home.
 

Brian Rupnow

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Gordon---On my rotary table there is a little swing lever that disengages the worm from the gear. There is also a threaded lock pin that when tightened down prevents the gear from being disengaged. If your crank was turning but the output wasn't, then probably that lever was disengaged.---Brian
 

Gordon

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That was the problem. I went back to the shop to check it out. I had to move the lock pin to get the hold down bolt in and some where in the process the lever got moved. Normally I mount the table horizontal so I do not get into that area.
 

SmithDoor

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It not hard to do with right tooling.
I have used 1144 steel at time it was 12 foot bar. Good news today you buy it by inch.
I would buy about 3" more so can chuck the part.
If it to short it is a pain to work.

What type tooling do you have?

Dave

That was the problem. I went back to the shop to check it out. I had to move the lock pin to get the hold down bolt in and some where in the process the lever got moved. Normally I mount the table horizontal so I do not get into that area.
 

Master

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Making a steel holder is my method although I thread it for a nut. Cast iron can make good gears. Make sure everything is tight. Disappointing when getting to the last teeth to find something slipped.
 

Peter Twissell

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If you have a tailstock, or you can Jerry rig something similar on the mill table, supporting the overhanging gear will make the set up a lot more rigid.
 

bobden72

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I just stripped a gear on an engine and now I have to make a new gear. The first gear was brass and obviously was not strong enough. I am making a new one out of steel. I just purchased a set of divider plates for my rotary table so that I could cut gears. This is great, now I get to play with my new toys. The gear is 2 1/2 OD with a hub and 3/8 bore. I am just about done with machining the blank and I started thinking about how I was going to hold the blank on the rotary table. In the past I have used my spin indexer which uses a 5C collet so as long as I left a hub which would fit in the collet or had a bore which I could adapt to the collet I could hold on to the blank. I have a 6" rotary table and have a 6" three jaw chuck mounted to the table. Unfortunately if I hold the blank in the chuck the cutter hits the chuck. I also have a 4" chuck which I could mount to the table but even that will not clear the cutter. Any ideas on how to hold this blank? How have others done this? The only thing I can come up with is to hold my hex 5C collet block in the three jaw chuck.
As you did before make a mandrel to fit the gear blank but long enough so when in the chuck the cutter will not touch the chuck. You will also need a support on the outer end to make it rigid, very much like a tail stock.
 

Thommo

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Turn a round piece of steel, about 1 1/2" diameter x 4" long. Put a reduced end on it to fit into the gear, but about 1/16" shorter than the length of the gear hub. Drill and tap the end of the steel for a 5/16" or a 3/8" thread. Mount the gear on the end, put a bolt in the end of the shaft and cinch it up tight. Now, hold the opposite end in the chuck. That way the gear will be far enough away from the chuck that the cutters won't touch the chuck jaws.
You’re one smart cookie Brian Rupnow. I love the way that you are ripping through that Tee head engine
 

Gordon

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Well not a good morning. Something is not square with the world. The cutter is cutting deeper on one side so the piece is obviously not centered on the table. I am not sure if the three jaw chuck is not centered or the 5C collet block is not seated properly or if the the chuck is not down flat on the table. I suspect that it is a combination but I think that it is mostly not being flat on the table because my preliminary measurements indicate the further I get away from the mill table the more the error. At the base of the chuck it appears to have about .005 run out. Where the blank is being cut it is about .050. Off the play around with indicators etc.
 

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SmithDoor

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Looks like a great job.

Dave

Well not a good morning. Something is not square with the world. The cutter is cutting deeper on one side so the piece is obviously not centered on the table. I am not sure if the three jaw chuck is not centered or the 5C collet block is not seated properly or if the the chuck is not down flat on the table. I suspect that it is a combination but I think that it is mostly not being flat on the table because my preliminary measurements indicate the further I get away from the mill table the more the error. At the base of the chuck it appears to have about .005 run out. Where the blank is being cut it is about .050. Off the play around with indicators etc.
 

Rdean33422

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Does your rotary table have a morse taper center?
This is the setup I usually use.
GEDC5323.JPG
The gear is pressed on to the morse taper and the OD is cut on the lathe. The taper is then held in the rotary table with a draw bar bolt in the rear. I also cut along the X axis using the auto feed so I don't have to turn the cranks.
I also made a block that is exactly the same height as the center line of the rotary table to set the cutter height.

Ray
 

Master

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Looks like you are pretty close. Wonder if the chuck is a tad off on the rotary
table. I would check the rotation of the chuck with a dial indicator. Maybe some foreign object in one of the jaws.
 

tornitore45

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Whatever holding method you use make sure it has a large flange because is difficult to keep a thin disk square when the bore is only 3/8" diameter.

As far as centering you have a 3 Jaw chuck mounted on the table holding what looks like a collet block. Lots of sources of error. If your RT has a morse hole a morse collet is your best bet.
 

Gordon

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I am in the process of recentering everything starting from the rotary table and every piece attached. I may not know where the actual error was located if I correct it while reinstalling everything. I think that the removable jaw on the chuck may not have been fully seated. The other suspect is the collet block. Lots of places for error. While going through this I am getting into things like cleaning the chuck. There are chips in the chuck and things are binding. The gear blank has a 1" dia hub so that is a better place to hold on to it than with the 3/8 bore. The table has a MT2 hole but it is difficult to mount to that because the blank must be extended out away from whatever holds it to provide clearance for the cutter. I am concerned about trying to hold a 2 1/2" dia piece by the 3/8 bore. My previous method of making the gear in the spin indexer has a lot fewer places for error but I just got the dividing plates and wanted to try that method. I made 9 gears for this project using the spin indexer and they all work just fine except that this one gear. I used a piece of oil impregnated brass that I had but it was too soft and stripped the teeth.
 

Richard Hed

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Well not a good morning. Something is not square with the world. The cutter is cutting deeper on one side so the piece is obviously not centered on the table. I am not sure if the three jaw chuck is not centered or the 5C collet block is not seated properly or if the the chuck is not down flat on the table. I suspect that it is a combination but I think that it is mostly not being flat on the table because my preliminary measurements indicate the further I get away from the mill table the more the error. At the base of the chuck it appears to have about .005 run out. Where the blank is being cut it is about .050. Off the play around with indicators etc.
Gordon,
I'm just curious, why do you have the indexing device facing into the mill body? I would think it would be easier to turn the indexer to the right by 90deg. You have the gear in such a position that it is difficult to see what is being cut, where the position of the cutter is, etc. It looks to me that the cutter position is too high or low and that is why the teeth being cut are at an improper angle. When I cut gears, I actually cut a tiny bit, say .005 all the way around to make sure everything is kosher. That is, it may be a pain to turn all these turns with the indexer, but I also don't make the mistake you made of being off center and cutting too deep on one side and too shallow on the other. Also, by making this first tiny cut, I can count my teeth and make sure I am not making "that" misteak of one extra or one too short of teeth. (I always mark the first tooth as "zero" then count all the way around, and count the marked, last tooth as the last tooth, so the first tooth (zero) is counted twice). the first tooth is NOT tooth number 1, it is 0. Beginners often make this mistake, I know I did.

I'm sure that there must be a chip or something somewhere in your setup. But first of all, I would turn that darned indexer so you can see what hyou are doing.
 

Gordon

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The reason why I have the setup at 90° is perhaps not a really valid reason but I did that because there was not enough room on the table to put the RT without removing the vise. If I removed that I would have to reset the vise so for the one project I thought that I would just live with the inconvenience of being in a less than optimal position. That being said that is not my problem. I found the problem. The three jaw chuck has .025 runout. I am not sure why it has not been a problem in the past because I have been using it for several years and I am pretty sure that I have checked it before. It is not a sprung scroll because I have checked it with a 1 dia shaft and a 1 1/2" dia shaft. Jaw #2 is about .030 further from center than #1 and #3. That is not enough to indicate the jaws in the wrong slot. I am pretty sure that the chuck is not repairable so I guess that means a new chuck.
 

Richard Hed

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The reason why I have the setup at 90° is perhaps not a really valid reason but I did that because there was not enough room on the table to put the RT without removing the vise. If I removed that I would have to reset the vise so for the one project I thought that I would just live with the inconvenience of being in a less than optimal position. That being said that is not my problem. I found the problem. The three jaw chuck has .025 runout. I am not sure why it has not been a problem in the past because I have been using it for several years and I am pretty sure that I have checked it before. It is not a sprung scroll because I have checked it with a 1 dia shaft and a 1 1/2" dia shaft. Jaw #2 is about .030 further from center than #1 and #3. That is not enough to indicate the jaws in the wrong slot. I am pretty sure that the chuck is not repairable so I guess that means a new chuck.
But earlier, you said it had tight spots, maybe chips in the scroll? Have you had it apart to clean? I can't understand how this could be that far off. I don't believe your chuck is bad, i thimpfk there must be some other problem. I had a four jaw that had one of the jaws very tight. I took it out and found that it was not centered properly when the teeth were cut. I told Grizz about it and they wanted to send a new, complete 4 jaw. I convinced them to send only the jaws themselves. They work fine and cost a lot less to ship.
 
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