Bob,
The process of locating with an indicator from the table is actually the most precise way to locate center (of the table), considering it's actually locating from the true rotational center, and not a mechanical feature of the table. However, had you not been able to release your table and be able to sweep the pin by hand, I think you can see how cumbersome that could be. [img]/ubb/images/graemlins/frown.gif"%20alt="[/img]
By locating the table as you do, you are at the mercy of the position of the pin, however. If you were to chuck up a pin with a drill chuck, you may be adding a respectable amount of error because you will be locating the table under the centerline of the pin, which may or may not be concentric with the spindle. Holding the pin in a collet certainly minimizes the chance of error, though it may not, and probably does not, eliminate it totally. I think you can see clearly that the best way to locate a rotary table is to spin the indicator from the spindle and have a feature on the table that is unchanging, such as the center hole, which is properly located on true center. That's its purpose, and it should be dead concentric with the center of rotation of the table. [img]/ubb/images/graemlins/cool.gif"%20alt="[/img]
The one big shortcoming of an eccentric bushing being that once the table is located under the spindle, you can't rely on the table center hole for locating parts or fixtures, the bad condition of Mosey's table that he is returning. [img]/ubb/images/graemlins/mad.gif"%20alt="[/img] That doesn't prevent using the table, certainly, but it does add time to setup. One should be able to rely on the center hole of the table, otherwise there is no good reason for it to exist. I liken the center hole that isn't in the center to a window that one can't see through. What's the point? [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]
Harold
Rotary Table Precision
Re: Rotary Table Precision
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Rotary Table Precision
You are right, the thing that makes my blood boil is every thing we buy has some sort of defect. I gess that I raise the white flag to fast and fix it my self. and with the venders out there it eats a lot of time...for fun try to get a refund or adjestment from ups for being late or braking something...Phil in mt
Re: Rotary Table Precision
Hi Phil,
Yep! It seems you can't buy anything of quality anymore, but we, as consumers, are partially responsible. If we didn't cave in to the suppliers, they'd quickly learn to change their ways or they'd be out of business, which is where they should be if they have a go to hell attitude towards the consumer.
I think it's appalling that we used to lead the world in quality, and now find ourselves unable to do anything right. In no small part is it the responsibility of each of us to step up to the plate and demand more than we are getting. We should also be prepared to give more than we have been giving. To me, it's embarrassing that we have become a nation of greedy, uncaring people, more interested in our personal gratification than the well being of our fellow man and the heath of our nation as a whole. Look back to the healthy attitude of our people during world war II and see the difference. We've lost a great deal in my opinion. Heavy, heavy sigh!! [img]/ubb/images/graemlins/frown.gif"%20alt="[/img]
As for UPS, I think they should be boycotted. Their attitude stinks, and their pay scale is killing the shipping industry. I'm having a hard time understanding why a truck driver is worth $10/hour more than a qualified tool & die man. Makes no sense. [img]/ubb/images/graemlins/mad.gif"%20alt="[/img]
Harold
Yep! It seems you can't buy anything of quality anymore, but we, as consumers, are partially responsible. If we didn't cave in to the suppliers, they'd quickly learn to change their ways or they'd be out of business, which is where they should be if they have a go to hell attitude towards the consumer.
I think it's appalling that we used to lead the world in quality, and now find ourselves unable to do anything right. In no small part is it the responsibility of each of us to step up to the plate and demand more than we are getting. We should also be prepared to give more than we have been giving. To me, it's embarrassing that we have become a nation of greedy, uncaring people, more interested in our personal gratification than the well being of our fellow man and the heath of our nation as a whole. Look back to the healthy attitude of our people during world war II and see the difference. We've lost a great deal in my opinion. Heavy, heavy sigh!! [img]/ubb/images/graemlins/frown.gif"%20alt="[/img]
As for UPS, I think they should be boycotted. Their attitude stinks, and their pay scale is killing the shipping industry. I'm having a hard time understanding why a truck driver is worth $10/hour more than a qualified tool & die man. Makes no sense. [img]/ubb/images/graemlins/mad.gif"%20alt="[/img]
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
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Michael_Az
- Posts: 407
- Joined: Sat Jan 04, 2003 10:07 am
- Location: Southeastern Az
Got a question for you Harold
Last week I bought a 8" Palmgren rotary from ebay. Appears to be new and unused. No marks anywhere. When I centered the table hole [1 5/8"] I noticed that one of the four points I was indicating in the hole is about 7 tenths out. How that happened, I dont know, it isn't egg shaped, as the other three points zero out. When I rotate the table 360 degrees with the indicator on the outside diameter of the table, its only about six tenths out of round. Should I center the table with the outside diameter and then skim the hole with a cutter to bring everything in? The way I see it, the hole size doesn't matter, just that everything is true.
Thanks
Michael
Thanks
Michael
Saimp 2 HP 10 X 44 mill, #2 Cin Horz Mill, Cholchester 13" lathe, LeBlond 15" Dual Drive.
Re: Got a question for you Harold
Hi Michael,
My hunch is that the hole is out of round. It's easy enough to make it read identically on three sides if you're using a .0005" reading indictor. If you were to split the reading that is long, wouldn't it read as if it's not round, with a few tenths on each side of the smaller dimension? Lots of half thou indicators tend to quit reading when they get around .0002" deflection, so it could be lying to you slightly.
In this case, I think I'd live with the error. In truth, it's only about .0003" off actual center, a far cry from the .003" that was reported on the Sherline table.
Contrary to your thoughts, the hole size is important. One of the accepted ways of making tooling for rotary tables is to make a locating pin that fits the center of the table, so once center is established, all one has to do is drop on the fixture and it's ready to use. If you open up the hole, you'll be stuck with a bastard size hole that would have a sloppy fit for standard sized pins, regardless of the size. You wouldn't be much farther ahead than you are now. My Bridgeport has a 1" bore, which makes it really nice because you can make a fixture that can go from a lathe collet to a dividing head to a rotary table and always be on center. Give that some thought before you alter the table.
The center bushing may be heat treated hard enough that you may not be able to cut it, so that is another consideration. What I'd do if it was mine and I couldn't live with the small amount of runout, which, for most work would be acceptable, is to remove the old bushing and make a new one that could be finished on location, holding the same size so you don't lose the ability to use the hole for standard pin size, what ever that size may be.
If, when you removed the bushing, you found the table hole was not round, but the bushing was and was being deformed by the table, you may be able to bore the table a minimum amount to round it out, but only after finding dead center, with the head of your mill dialed dead true (trammed, perpendicular). You could then make a thin walled bushing and re-install the same center busing in the now round hole, which would round up the bushing when it was installed. It's hard to say why the hole is not dead round, but it could be from movement of the cast iron after being machined. I doubt very much that any of the castings these days are subjected to any kind of normalizing or aging that they sorely need to be stable. That you found the perimeter of the table out a similar amount sure raises questions. It could have also been produced on a machine that has a tremendous amount of runout. That's the hazard of a spindle that doesn't track center.
I'd be interested in hearing from you when you've made your decision and done what ever it is that you intend to do.
One word. Don't expect milling machine devices to be dead true. You don't pay enough for them to expect that, they aren't made the way jig borer components are made.
The amount of error you report, while not great, is likely to be in spec, whereas the huge amount on the Sherline, especially considering it is a miniature table, was totally unreasonable.
Harold
My hunch is that the hole is out of round. It's easy enough to make it read identically on three sides if you're using a .0005" reading indictor. If you were to split the reading that is long, wouldn't it read as if it's not round, with a few tenths on each side of the smaller dimension? Lots of half thou indicators tend to quit reading when they get around .0002" deflection, so it could be lying to you slightly.
In this case, I think I'd live with the error. In truth, it's only about .0003" off actual center, a far cry from the .003" that was reported on the Sherline table.
Contrary to your thoughts, the hole size is important. One of the accepted ways of making tooling for rotary tables is to make a locating pin that fits the center of the table, so once center is established, all one has to do is drop on the fixture and it's ready to use. If you open up the hole, you'll be stuck with a bastard size hole that would have a sloppy fit for standard sized pins, regardless of the size. You wouldn't be much farther ahead than you are now. My Bridgeport has a 1" bore, which makes it really nice because you can make a fixture that can go from a lathe collet to a dividing head to a rotary table and always be on center. Give that some thought before you alter the table.
The center bushing may be heat treated hard enough that you may not be able to cut it, so that is another consideration. What I'd do if it was mine and I couldn't live with the small amount of runout, which, for most work would be acceptable, is to remove the old bushing and make a new one that could be finished on location, holding the same size so you don't lose the ability to use the hole for standard pin size, what ever that size may be.
If, when you removed the bushing, you found the table hole was not round, but the bushing was and was being deformed by the table, you may be able to bore the table a minimum amount to round it out, but only after finding dead center, with the head of your mill dialed dead true (trammed, perpendicular). You could then make a thin walled bushing and re-install the same center busing in the now round hole, which would round up the bushing when it was installed. It's hard to say why the hole is not dead round, but it could be from movement of the cast iron after being machined. I doubt very much that any of the castings these days are subjected to any kind of normalizing or aging that they sorely need to be stable. That you found the perimeter of the table out a similar amount sure raises questions. It could have also been produced on a machine that has a tremendous amount of runout. That's the hazard of a spindle that doesn't track center.
I'd be interested in hearing from you when you've made your decision and done what ever it is that you intend to do.
One word. Don't expect milling machine devices to be dead true. You don't pay enough for them to expect that, they aren't made the way jig borer components are made.
The amount of error you report, while not great, is likely to be in spec, whereas the huge amount on the Sherline, especially considering it is a miniature table, was totally unreasonable.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
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Michael_Az
- Posts: 407
- Joined: Sat Jan 04, 2003 10:07 am
- Location: Southeastern Az
Re: Got a question for you Harold
Hey, thanks Harold. Of course your right about it being egg shaped, I should of thought of that myself. I was just reading it all on one side. I think your right about leaving it alone. Three tenths isn't much. Another thing you might have informed me about is the bushing. I don't have one! I didn't know they come with the table. I just have a 1 5/8 hole. I am going to make one, or maybe several with different size holes. I have an extra three jaw chuck and four jaw that would work well with the table and they don't fit anything else I have. If I remember right they are 1 1/2"X 8 TPI. Would it be a good idea to make a short spindle to screw into the chucks with a slip fit on the other end for the bushing in the table? I am thinking there would have to be a plate between the chuck and table so it could be bolted down. Is this sounding convuluted?
Thanks for the good advise.
Michael
Thanks for the good advise.
Michael
Saimp 2 HP 10 X 44 mill, #2 Cin Horz Mill, Cholchester 13" lathe, LeBlond 15" Dual Drive.
Re: Got a question for you Harold
A plug with a thread to fit your chuck will center the chuck o.k., but you still need a way to prevent rotation, and hold the thing on [img]/ubb/images/graemlins/confused.gif"%20alt="[/img] If your R/T is a larger Ø than the chuck, one method that works well is to make a new backplate for the chuck. The backplate should be larger in Ø than the chuck by a couple inches or so to allow a bolt pattern to match the T-slots in the R/T. The backplate should also have a short pilot to locate it on your R/T. A short key on the bottom side of the backplate to match one of the R/T T-slots will prevent the chuck from rotating. This is probably easier to make than a threaded plug, and should line up the chuck as good, if not better.
Re: Got a question for you Harold
Michael,
Now you're really talking! Without a bushing, you're wide open. Yeah, I think I would bore it, but I'd get my ducks in a row first, and when I was finished I'd have a heat treated busing that was pressed in so center would be reliable, and of a diameter that it could be used as I suggested. It makes setting up tooling very easy.
I don't think I'd recommend you use the cast iron surface for a slip fitting. It wouldn't take much to have the bushing hole loosened up, at which time it wouldn't be of much use. If you would like to have various devices, you would be better served to have a fixed, heat treated bushing to which all your tooling fits. That's the idea of the center bushing.
As far as your chucks go, I'd make an adapter that locates from the thread of the chuck to the hole size, or I'd remove the backing plate and make one that is large enough to bolt to the rotab using the T slots., with a pin dead on center, which would fit the hole in the table. This plate could be the same diameter as your rotab. The chuck would mount with screws from the bottom side of the adapter plate, matching the original mounting holes for the backing plate, using socket head cap screws in counterbored holes. Your adapter plate would have to be thick enough to acccomodate your screws, probably 3/4". This is the best way to go, because it keeps the overall height reasonable and the chuck very rigid. The adapter plate can be aluminum if desired.
I think you can see how nice it is to just slip a chuck on the rotab and not worry about center. That's the value of the center hole being in the right place.
If you don't have the ability to make a heat treated and ground bushing, you might consider using a drill busing in its place, then make the adapter bushing to fit the drill bushing to the rotab. If you choose this route, keep in mind that a few tenths makes for a good press fit, and if you go much beyond .0005" press you're likely to collapse the bushing so it won't accept a 1" pin, if that is the size you choose to use. I'd not go any larger than 1-1/8" because that's the limit of 5C collets.
To find center of your table, you'll have to dial from the table to the spindle. Put a mag base on the table with the indicator near center, then dial either the taper in the quill, or a pin that has been installed and checked for concentricity before you use it for a center reference. You'd find center of the table by turning the table, not the spindle. Make sure you understand this.
You're trying to remove a very small amount of error here and it will be easy to introduce a like amount by doing something as simple as touching a locking handle on your mill. Be certain that the center of the table is established with the locks on the table and saddle set. Position generally changes slightly when you set them. Again, be certain that your mill head is dialed dead perpendicular. Don't make any fast moves, think it through carefully and you can end up with a bushing that is within a couple tenths of dead center. This kind of work requires good thinking.
Good luck~
Harold
Now you're really talking! Without a bushing, you're wide open. Yeah, I think I would bore it, but I'd get my ducks in a row first, and when I was finished I'd have a heat treated busing that was pressed in so center would be reliable, and of a diameter that it could be used as I suggested. It makes setting up tooling very easy.
I don't think I'd recommend you use the cast iron surface for a slip fitting. It wouldn't take much to have the bushing hole loosened up, at which time it wouldn't be of much use. If you would like to have various devices, you would be better served to have a fixed, heat treated bushing to which all your tooling fits. That's the idea of the center bushing.
As far as your chucks go, I'd make an adapter that locates from the thread of the chuck to the hole size, or I'd remove the backing plate and make one that is large enough to bolt to the rotab using the T slots., with a pin dead on center, which would fit the hole in the table. This plate could be the same diameter as your rotab. The chuck would mount with screws from the bottom side of the adapter plate, matching the original mounting holes for the backing plate, using socket head cap screws in counterbored holes. Your adapter plate would have to be thick enough to acccomodate your screws, probably 3/4". This is the best way to go, because it keeps the overall height reasonable and the chuck very rigid. The adapter plate can be aluminum if desired.
I think you can see how nice it is to just slip a chuck on the rotab and not worry about center. That's the value of the center hole being in the right place.
If you don't have the ability to make a heat treated and ground bushing, you might consider using a drill busing in its place, then make the adapter bushing to fit the drill bushing to the rotab. If you choose this route, keep in mind that a few tenths makes for a good press fit, and if you go much beyond .0005" press you're likely to collapse the bushing so it won't accept a 1" pin, if that is the size you choose to use. I'd not go any larger than 1-1/8" because that's the limit of 5C collets.
To find center of your table, you'll have to dial from the table to the spindle. Put a mag base on the table with the indicator near center, then dial either the taper in the quill, or a pin that has been installed and checked for concentricity before you use it for a center reference. You'd find center of the table by turning the table, not the spindle. Make sure you understand this.
You're trying to remove a very small amount of error here and it will be easy to introduce a like amount by doing something as simple as touching a locking handle on your mill. Be certain that the center of the table is established with the locks on the table and saddle set. Position generally changes slightly when you set them. Again, be certain that your mill head is dialed dead perpendicular. Don't make any fast moves, think it through carefully and you can end up with a bushing that is within a couple tenths of dead center. This kind of work requires good thinking.
Good luck~
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
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captainkirk
Re: Rotary Table Precision
I see your point about it being more convenient to do it the way you suggest, but if people don't hold manufacturers feet to the fire to produce good quality products then they will degrade in time to "good enough" practices. Now all their products and all the products made by the people that use their machines will degrade over time. I agree with fixing small problems yourself but if the product was non useable as it left the factory I would do everything in my power to have them make it right. Pressure to do it over at a higher cost will force them to do it right the first time. It's economics at that point, so when you make them responsible you help everyone after you to get a better product. In this case I suspect this type of garbage isn't normal for sherline as I think most people seem to think highly of them, and some of the stuff that comes off of them is just plain beautiful. I have done what you suggest in the past and always felt cheated by the company that I bought it from for a long time. I still feel that "Made In U.S.A." should stand for quality and every compromise from that stance degrades the system more every day. I was once told "Build it as if your Grandfather was looking over your shoulder" and if your company doesn't appreciate it then move to another company that will, this creates a self improving system. I don't level this directly at you so please don't take offence, it's leveled at all of us. If anyone out there in a manufacturing/ building role feels different please forward your thoughts so I may steer clear of your products....tirade over....(mostly)
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Michael_Az
- Posts: 407
- Joined: Sat Jan 04, 2003 10:07 am
- Location: Southeastern Az
Re: Got a question for you Harold
Thanks Harold and Jeff for all this info, I'm saving it. I did forget to mention the two chucks I have, have different backs. One is the familiar full back and the other has a smaller partial back that doesn't cover the back completely. Guess I'll make an adapter for each. I did rumage through my scrap today and found a piece of tool steel 8 1/2 diameter. I understand what you describe Harold and I will do it like that. I don't have a furnace nor a grinder, so maybe a store bought bushing might work well. Here is a picture of the table. I went through my tool catalogs and every maker of rotarys show a bushing with the table except Palmgren. I guess they don't include the bushing. www.zekes.com/~milkman/rotarytable.jpg
Thanks
Michael
Thanks
Michael
Saimp 2 HP 10 X 44 mill, #2 Cin Horz Mill, Cholchester 13" lathe, LeBlond 15" Dual Drive.
Re: Rotary Table Precision
In a way we can blame ourselfs, The first thing we do is seek out the cheapest price on what ever we need, so the importers buy the cheapest. Even the stuff made in china could be good even real good if the importers would bring it over, thay choose to import the junk because there profit is better. If we made the importers replace the out of spec tools thay would buy the higher value tools to advoid the truble. Likewise if the imports cost more the high end suppliers would do a better job as there would be more profit to do so. It would also be nice if we could buy from the local supply store then a return would be easy, but when thay make 30% for a phone call we buy from the mail order stores and return becomes a problem.
And of corse you have sales people that dont care, and will say anything to make you go away. I dont know what to do, I do know that when something goes wrong with the parts we build we make it right or we dont get the mans work agin
and wont be paid for what work we did do for him.Probly what we should do is when we buy junk send it back for refund and buy from some other supplier and let the first vender know why...Phil in MT
And of corse you have sales people that dont care, and will say anything to make you go away. I dont know what to do, I do know that when something goes wrong with the parts we build we make it right or we dont get the mans work agin
and wont be paid for what work we did do for him.Probly what we should do is when we buy junk send it back for refund and buy from some other supplier and let the first vender know why...Phil in MT
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captainkirk
Re: Rotary Table Precision
I agree with you wholeheartedly, money drives results. I think at the very least we should drive the tool purveyors to provide specifications on the tooling they offer.
I hear your frustration and see the poor quality of the tooling being offered for sale, and can only conclude that the importers are getting this stuff dirt cheap to market it to the unwary. When I see a post from someone new to this industry asking about this Mill/drill from China or that small "Mini Mill/ lathe I cringe because I know they probably don't posess the skills to repair what is going to be wrong with it when it arrives, and these very people are going to be most of the life blood for the future of manual machining. I can only hope it doesn't leave to bad a taste in their mouths so they take their efforts elsewhere. We havn't even touched on the unreputable Used Equipment sales people, trying to sell completely useless worn out junk as "High Quality Made In U.S.A." To some extent I can excuse the "Importers" as business men selling lower end quality China tools/tooling as a viable business venture to provide low cost solutions to a group of consumers that can't afford the good quality equipment. They provide a service that fits a need. The used equipment sales person is blatantly ripping off the unwary "Newby" knowing the things a piece of crap. I have found you have a better chance of getting help with the purchase of the cheaper made in China stuff than the Used equipment guy, at best this area of the machine tool industry is frought with trouble no matter which way you go......Let the buyer beware. It has been a good discussion and the more we share our information the better it can be for all involved.
I hear your frustration and see the poor quality of the tooling being offered for sale, and can only conclude that the importers are getting this stuff dirt cheap to market it to the unwary. When I see a post from someone new to this industry asking about this Mill/drill from China or that small "Mini Mill/ lathe I cringe because I know they probably don't posess the skills to repair what is going to be wrong with it when it arrives, and these very people are going to be most of the life blood for the future of manual machining. I can only hope it doesn't leave to bad a taste in their mouths so they take their efforts elsewhere. We havn't even touched on the unreputable Used Equipment sales people, trying to sell completely useless worn out junk as "High Quality Made In U.S.A." To some extent I can excuse the "Importers" as business men selling lower end quality China tools/tooling as a viable business venture to provide low cost solutions to a group of consumers that can't afford the good quality equipment. They provide a service that fits a need. The used equipment sales person is blatantly ripping off the unwary "Newby" knowing the things a piece of crap. I have found you have a better chance of getting help with the purchase of the cheaper made in China stuff than the Used equipment guy, at best this area of the machine tool industry is frought with trouble no matter which way you go......Let the buyer beware. It has been a good discussion and the more we share our information the better it can be for all involved.