It Using Pins to Locate Tram on a Mill—-how does this work out in practice?
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    Default It Using Pins to Locate Tram on a Mill—-how does this work out in practice?

    In a another current thread a poster mentioned tha Beaver mills used pins to positively locate nod and inclination of their mill heads. I have long mused about adding such tapered locating pins to my BP head. I thought I’d start a new thread here rather than derail that thread

    First a couple questions:
    1) I assume that taper pins are used in that application.
    2) What size pins are used?
    3) In actual practice how accurately do they tram the head?

    I am wondering if pins would provide the degree of accuracy that I like to achieve when face milling things like straight edges. I find that the difference between a nice crosshatch flat pattern from my face mail versus a slightly concave pattern can be a matter of only maybe 5 thousandths of movement of the Facemail when measured against the table as I pivot the head slightly. I wonder if that tiny increment of rotation would be locked in that accurately by a pin or not. Or does the pin provide a pretty close approximation of trim which in the final analysis has to be touched up a bit anyway to get really accurate tram?


    I suppose one disadvantage of the pin might be that in the event the cutter encounters unexpected resistance, a pin would prevent slight rotation which can prevent a more serious crash should such pressure-relieving rotation not be possible.


    Anyway, I’m interested in pertinent thoughts and experience on the subject.


    Denis

    If my math is correct, rotating the head enough for a .005” deflection on a roughly 20” arm is a 2 arc-second rotation. A common precision level uses a 20 arc-second vial.

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    .005" in 20" is more like 51.5 arc-seconds. Pins will get you pretty close if they're done right. And I'd probably use tapered pins, not straight. You can use the pins for alignment, clamp the head down and then remove the pins if you're worried about crash damage.

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    Quote Originally Posted by eKretz View Post
    .005" in 20" is more like 51.5 arc-seconds. Pins will get you pretty close if they're done right. And I'd probably use tapered pins, not straight. You can use the pins for alignment, clamp the head down and then remove the pins if you're worried about crash damage.
    eKretz, thank you.

    Yes, I rechecked my calculations and you are embarrassingly correct about the 51 arc seconds. Not sure what went sideways with my first time through.

    The idea of removing the pins after setup occurred to me and is what I would do. Simply drilling and tapping the large end of the pin would allow for convenient removal and I see drilled and tapped pins are commercially available though what I found are made of 12L14 or stainless.

    It seems like in this application that the pin used in quite soft grey iron, should be a hardened as soft on soft is usually not a good design feature. .I expect that I would need to turn and tap a pin from tool steel and then harden it. Finally I would grind it and finally part it from the bar. All very doable.

    Still listening.

    Denis

    My intuition suggests using a pin on the order of 1/2" diameter.

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    Quote Originally Posted by dgfoster View Post
    eKretz, thank you.

    Yes, I rechecked my calculations and you are embarrassingly correct about the 51 arc seconds. Not sure what went sideways with my first time through.

    The idea of removing the pins after setup occurred to me and is what I would do. Simply drilling and tapping the large end of the pin would allow for convenient removal and I see drilled and tapped pins are commercially available though what I found are made of 12L14 or stainless.

    It seems like in this application that the pin used in quite soft grey iron, should be a hardened as soft on soft is usually not a good design feature. .I expect that I would need to turn and tap a pin from tool steel and then harden it. Finally I would grind it and finally part it from the bar. All very doable.

    Still listening.

    Denis

    My intuition suggests using a pin on the order of 1/2" diameter.
    Pins are not accurate enough. When accuracy is an issue like the 2nd ( 3rd ) head of SIP Jig borer one locks the angle with a dead stop which is adjustable. Or can be filed. I tend to remember pins as being around 3/4" . Now that I remembered : when you take apart a Jig Borer there will be a lot of pins. When you put it back, nothing will fot 100% and you have to adjust and ream - that's why that nut seems to be there for no reason.

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    Quote Originally Posted by Orbital77 View Post
    Pins are not accurate enough. When accuracy is an issue like the 2nd ( 3rd ) head of SIP Jig borer one locks the angle with a dead stop which is adjustable. Or can be filed. I tend to remember pins as being around 3/4" . Now that I remembered : when you take apart a Jig Borer there will be a lot of pins. When you put it back, nothing will fot 100% and you have to adjust and ream - that's why that nut seems to be there for no reason.
    Thanks.

    I see the logic and convenience of an adjustable dead stop over a drilled and reamed setup that has to wear with use and is not easily adjusted on the fly.

    The second reason the dead stop might be preferable is that since starting this thread, I went out and examined the BP tilt and nod mechanisms. Particularly on the tilt there is no obvious place that an accessible decent-sized taper pin could be placed that I could see. But a couple of dead-stop bosses could be added to the tilt without a great deal of trouble. The.nod would accommodate a sizable pin fairly easily.

    Denis

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    A dead stop won't be more accurate than well-fitted tapered pins of a size that won't easily flex. Note that the other poster mentioned an "adjustable" dead stop. There is always some clearance in a pivot, a dead stop can leave that clearance on one side or the other or somewhere in the middle. An adjustable dead stop is not really any better than just using the original mechanism that's already in place.

    Tapered pins implemented correctly and kept clean will positively locate pretty damned accurately. If you don't keep both the pins and pin holes clean, or if you use pins that aren't straight or that are dinged up, obviously there will be problems. Personally, I'd just stick to the original method... Tramming a head in on a vertical mill doesn't take that long at all.

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    Quote Originally Posted by dgfoster View Post
    eKretz, thank you.

    Yes, I rechecked my calculations and you are embarrassingly correct about the 51 arc seconds. Not sure what went sideways with my first time through.

    The idea of removing the pins after setup occurred to me and is what I would do. Simply drilling and tapping the large end of the pin would allow for convenient removal and I see drilled and tapped pins are commercially available though what I found are made of 12L14 or stainless.

    It seems like in this application that the pin used in quite soft grey iron, should be a hardened as soft on soft is usually not a good design feature. .I expect that I would need to turn and tap a pin from tool steel and then harden it. Finally I would grind it and finally part it from the bar. All very doable.

    Still listening.

    Denis

    My intuition suggests using a pin on the order of 1/2" diameter.
    If you intend making your own pins I'd suggest making them out of square bar and leaving a square on one end. That way you can easily extract them by turning the pin with a spanner ( wrench ) on the square. All " Alfred Herbert " machines had taper pins made in this fashion.

    Using pins to " Zero " up the head is a good idea in my opinion. On a double adjustment style head like a " Bridgeport " it'll save you a fair bit of time.

    Regards Tyrone.

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    Quote Originally Posted by Tyrone Shoelaces View Post
    If you intend making your own pins I'd suggest making them out of square bar and leaving a square on one end. That way you can easily extract them by turning the pin with a spanner ( wrench ) on the square. All " Alfred Herbert " machines had taper pins made in this fashion.

    Using pins to " Zero " up the head is a good idea in my opinion. On a double adjustment style head like a " Bridgeport " it'll save you a fair bit of time.

    Regards Tyrone.
    Tyrone, thank you.

    The square pin head idea is something I was unaware of and sounds like a very nice enhancement of pin function. Giving such a pin a quarter turn with a spanner would be much more convenient and quicker than screwing in a bolt to then use to knock loose or jack out the pin. Obviously, the small end will be buried in the casting. And these pins would be installed and removed with some regularity. In fact, having pins might overcome some reluctance I have to rotate the head on occasion when doing so would be the ideal approach to say cleaning up the finger recess on one of the straight edges that I cast. Yes, I'll rotate when it is what NEEDS to be done. But, sometimes I'll get by with a ball end mill run vertically (not necessarily ideal) rather than knock my mill out of tram and then have to futz around retramming.

    As an aside, I have found that using a 3 inch face mill helps me establish precise functional tram quicker than swinging an Indicol. I have seen various two-indicator rigs to be chucked in the mill, but using the face mill to get close by just rotating it by hand and then taking a light cut and observing the pattern made on the test piece has been the most sure-fire method I've used. Probably just indicates my general limitations. But works for me.

    Denis

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    The threaded hole is actually pretty darn quick. The key is to use a stack of washers or a spacer with hole size larger than the pin high enough to clear the top of the pin plus a little bit, say ⅛", then one washer on top with the hole just large enough to let the screw thread pass through. Screw the fastener in and it pulls the pin out. The square head would work pretty good too as long as the pins aren't driven in too tight. Some extra potential for wear though I'd think on pins that will be frequently in and out of the holes since you'd need to rotate them to bust them loose.

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    Quote Originally Posted by eKretz View Post
    The threaded hole is actually pretty darn quick. The key is to use a stack of washers or a spacer with hole size larger than the pin high enough to clear the top of the pin plus a little bit, say ⅛", then one washer on top with the hole just large enough to let the screw thread pass through. Screw the fastener in and it pulls the pin out. The square head would work pretty good too as long as the pins aren't driven in too tight. Some extra potential for wear though I'd think on pins that will be frequently in and out of the holes since you'd need to rotate them to bust them loose.
    A simple question well considered reveals many facets to be pondered. Good points.

    Denis

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    Should you also put a pin at common angles you use a lot? Probably better to drill them all before using the tapered reamer if you do want that option....

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    Quote Originally Posted by Rob F. View Post
    Should you also put a pin at common angles you use a lot? Probably better to drill them all before using the tapered reamer if you do want that option....
    Are you serious?

    Denis

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    Quote Originally Posted by dgfoster View Post
    Are you serious?

    Denis
    If you are always going back and forth from the same angle and perfect tram then why not have a pin to quickly set the angle, the same as you want a pin to quickly set the tram.
    IF you decide this is a good idea to save you some set up time it would seem easier to drill the hole with the machine at tram and then, set the head at your common angle, drill through the outer hole, using it to guide the drill. Then taper ream the holes. Just seems easier to locate the inner hole through a drilled hole as a guide than through a loose taper outer hole if you want to add it later. Reaming the second holes inner half should be easy to keep the reamer centered in the taper bore of the outer half, so as not to change the angle of the first hole.

    I would make bolt on stops with fine adjusting screw if it was mine though. I've seen enough tools with alignment pin holes that are no longer aligned as tool wears....

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    Quote Originally Posted by eKretz View Post
    The threaded hole is actually pretty darn quick. The key is to use a stack of washers or a spacer with hole size larger than the pin high enough to clear the top of the pin plus a little bit, say ⅛", then one washer on top with the hole just large enough to let the screw thread pass through. Screw the fastener in and it pulls the pin out. The square head would work pretty good too as long as the pins aren't driven in too tight. Some extra potential for wear though I'd think on pins that will be frequently in and out of the holes since you'd need to rotate them to bust them loose.
    I've removed taper pins that way in a pinch. 99% of the time I used my slide hammer though.

    I honestly preferred the square headed pins, being " Sir Alfred Herbert " they were hardened and ground all over,I never had any trouble removing them. The stubborn ones might need a 10" adjustable instead of a smaller spanner but that was it.

    The swivel heads on " Webster & Bennett " vertical boring machines had a similar dowel setting but the dowel had a hexagon head. They had a belt and braces system, a dowel and a " touch strip ". When the two faces of the touch strip were back in line you were set up for a perfect bore.

    Regards Tyrone.

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    Quote Originally Posted by eKretz View Post
    A dead stop won't be more accurate than well-fitted tapered pins of a size that won't easily flex. Note that the other poster mentioned an "adjustable" dead stop. There is always some clearance in a pivot, a dead stop can leave that clearance on one side or the other or somewhere in the middle. An adjustable dead stop is not really any better than just using the original mechanism that's already in place.

    Tapered pins implemented correctly and kept clean will positively locate pretty damned accurately. If you don't keep both the pins and pin holes clean, or if you use pins that aren't straight or that are dinged up, obviously there will be problems. Personally, I'd just stick to the original method... Tramming a head in on a vertical mill doesn't take that long at all.
    That is true : a dead stop won't be more accurate than any other thing as good as a dead stop.....

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    Quote Originally Posted by dgfoster View Post
    Thanks.

    I see the logic and convenience of an adjustable dead stop over a drilled and reamed setup that has to wear with use and is not easily adjusted on the fly.

    The second reason the dead stop might be preferable is that since starting this thread, I went out and examined the BP tilt and nod mechanisms. Particularly on the tilt there is no obvious place that an accessible decent-sized taper pin could be placed that I could see. But a couple of dead-stop bosses could be added to the tilt without a great deal of trouble. The.nod would accommodate a sizable pin fairly easily.

    Denis
    Whichever system, what matters is that adjustments must be 1) possible and 2) one-dimensional .

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    If you are using a 3" face mill to "tram" your head in what's the sense of going through all the trouble of putting pins into the head...it's obvious accuracy is not job one or even two at that matter. I spin an inducol on a purpose made piece of ground 410 stainless "it fits between the jaws of a kurt 6" when fully open"...0-0-0-0 is the goal but .0005 on one side is usually good enough and doesn't take much time.

    I'm not poking fun, just trying to save you a bunch of work.

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    Quote Originally Posted by plastikdreams View Post
    If you are using a 3" face mill to "tram" your head in what's the sense of going through all the trouble of putting pins into the head...it's obvious accuracy is not job one or even two at that matter. I spin an inducol on a purpose made piece of ground 410 stainless "it fits between the jaws of a kurt 6" when fully open"...0-0-0-0 is the goal but .0005 on one side is usually good enough and doesn't take much time.

    I'm not poking fun, just trying to save you a bunch of work.
    Actually getting the tram set as accurately as possible is quite important to me.

    You may have noticed I italicized the word “functional” when talking about face milling above. That might be different than optimal tramming for boring or drilling. Crazy? Might be. But, my machine and probably most machines have imperfect bearings and bedways. As BP’s go, I think mine are very good, but still imperfect. So, the tram of the mill’s head must shift ever so slightly when the side loading force of a face mill is applied This is not so evident, though it must actually be greater, when taking heavier cleanup cuts as the surface finish is fairly coarse and tram set “perfectly“ with the Indicol results in a cross-hatched pattern that suggests the mill was cutting flat. However, on my final light finishing cuts, the mill now may cut slightly toed into the direction of feed so that only the grooves from the lead side show on the part this being due to side load on the bearing actually making a visible difference. That is the point where I may tweak tram to get the nice aesthetically pleasing fine cross-hatch pattern. The actual difference in flatness on a 3” wide Straight Edge sole is difficult to measure and is “functionally“ insignificant. But that pattern is something my customers immediately notice and comment on in a positive way. So, I have found ways to achieve it in my shop.

    Now, if I need to bore an accurately vertical and round hole, forces on spindle bearings are radially symmetric and, if the bed does not move much for a second hole, play in bedways is no longer a factor. So a mathematically “ perfect” tram is also an ideal functional tram. So, the Indicol swung on a 6” diameter bearing race and some care will get me a mathematically accurate and functionally optimal hole alignment good enough for anything I need to do.

    Denis

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    One pin per joint would be limited to the accuracy of the fit of the machines joint...
    Two would be better three pins per joint would be best

    I think one pin per joint to get you close is a reasonable idea

    But if I was constantly going back and forth say from 0 to 45° I would really look at a fixture that had the proper angles built in

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    Quote Originally Posted by Tyrone Shoelaces View Post
    The swivel heads on " Webster & Bennett " vertical boring machines had a similar dowel setting but the dowel had a hexagon head. They had a belt and braces system, a dowel and a " touch strip ". When the two faces of the touch strip were back in line you were set up for a perfect bore.

    Regards Tyrone.
    I’m having trouble visualizing the touch strip. What was that like?

    Denis


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