Horizontal tombstone on vertical mill

[QuinnSjoblom]

Had an idea for a way to set up small scale production on some of the parts I do. Small aluminum parts, mostly within 2 or 3 inches square, all have edge drilling and other side features which require at least 4 setups to complete without 4th axis. My idea is to mount a horizontal tombstone on my 4th axis with a sort of tail stock support for rigidity. Was thinking just a solid chunk of aluminum maybe 3 or 4 inches square by maybe 12 to 16 inches long. Parts can be loaded on all 4 sides with pitbull clamps. This would allow for a good number of parts in a small area while also giving access to the edges of the part as the tombstone rolls. This knocks down 3 setups into 1. Still need 1 more setup to finish the back of the part, but 2 setups total instead of 4.
I've searched around and cant find anybody that does this. Is there a reason why? I cant see why it wouldn't be an effective way to do things. Same principle as a more common tombstone in a horizontal mill, but flipped 90 to run in a vertical mill with end support

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[Jim Dawson]

Can't see why it wouldn't work. A friend of mine was talking about doing this for the same reasons you describe, but not sure if he ever did it.

[deadlykitten]

hello quinn, it is a nice idea, and maybe is cheaper if you craft it yourself

once you start using it, all faces have to index pretty parallel to the main vmc table, thus is not critical to have 4 sides, or the section to be a square; it may be a random triangle, etc, but all the perpendicular sections, across it's length, have to be located at same distance from the vmc table ... it may be an idea to finish it on the 4th axis, so to achieve these conditions even so, this finish operation requires preparatory time, so to be sure that, after you finish it, and remove everything from the table, you can put it all back and achieve same tolerances ... you have to obtain fixture position repetability, thus, when you start machining this tombstone (or at least the finish pass), be sure that :
... machine is alligned : table not tilted, spindle perpendicular on the table, etc
... 4th axis is spinning arround an axis paralel to X axis ( = reference axis )
... tailstock axis is pretty colinear with the "reference axis"
... so far, if you take down the 4th axis + tailstock, and put them back on the machine, all alignment values have to be pretty equal, otherwise you don't achieve repetability
... now clamp the tombstone, and be sure that this new setup does not change the orientation of the "reference axis"; for example, tailstock may move when clamping, because :
...... tombstone center is forcing it to, because it is not aligned
...... some random plays, random clearances, etc

if these stuff is not checked, then each time you put the tombstone inside the machine, it will be in a different position, and the range will be wide enough to make someone lose time with realigning it every time; even if all is done ok, still the table will be at different positions, but the range will be shorter, and the range value can be predicted if all above steps are done ok

however, let's say that you end-up with the wide - range; if you craft small parts, then the range will get shorter, thus there will be less deviation/part, but overall, it will be the same; for example, if the table is tilted 0.3mm/1000mm, then you can not deliver a long part ( 800mm ) that requires 0.05 paralelism between faces, but you could deliver it if the part would be shorter, like shorter then 100mm


well, i guess you know, is all about tolerances, repetablity expected / desired tolerance, and crafting it with low costs

---

one more thing : when you raise a part from the vmc table, you lose rigidity, and you won't be able to machine it at identical specs; if the part will be on that 4th axis tombstone, it won't be like it is securely in a vice on the table, so you shave time with less human/operator intervention between setups, but you lose time with lower specs

so, if you wish for your tombstone to be more rigid, check this tips :
... change aluminium to cast steel ( vibration dampening )
... make it shorter ( less buckling )
... make it thicker ( so put more parts around it's circumference, not across it's length )
* secure it nice to the 4th axis, because, in the end, is all about the rigidity of the 4th axis

can you share the part that you are machining now, and your actual fixtures, for each setup ? who knows, maybe someone will have a nice idea

i hope you find it usefull / kindly

[QuinnSjoblom]

hello quinn, it is a nice idea, and maybe is cheaper if you craft it yourself

once you start using it, all faces have to indexed pretty parallel to the main vmc table, thus is not critical to have 4 sides, or the section to be a square; it may be a random triangle, etc, but all the perpendicular sections, across it's length, have to be located at same distance from the vmc table ... it may be an idea to finish it on the 4th axis, so to achieve these conditions even so, this finish operation requires preparatory time, so to be sure that, after you finish it, and remove everything from the table, you can put it all back and achieve same tolerances ... you have to obtain fixture position repetability, thus, when you start machining, be sure that :
... machine is alligned : table not tilted, spindle perpendicular on the table, etc
... 4th axis is spinning arround an axis paralel to X axis ( = reference axis )
... tailstock axis is pretty colinear with the "reference axis"
... so far, if you take down the 4th axis + tailstock, and put them back on the machine, all alignment values have to be pretty equal, otherwise you don't achieve repetability
... now clamp the tombstone, and be sure that this new setup does not change the orientation of the "reference axis"; for example, tailstock may move when clamping, because :
...... tombstone center is forcing it to, because it is not aligned
...... some random plays, random clearances, etc

if these stuff is not checked, then each time you put the tombstone inside the machine, it will be in a different position, and the range will be wide enough to make someone lose time with realigning it every time; even if all is done ok, still the table will be at different positions, but the range will be shorter, and the range value can be predicted if all above steps are done ok

however, let's say that you end-up with the wide - range; if you craft small parts, then the range will get shorter, thus there will be less deviation/part, but overall, it will be the same; for example, if the table is tilted 0.3mm/1000mm, then you can not deliver a long part ( 800mm ) that requires 0.05 paralelism between faces, but you could deliver it if the part would be shorter, like shorter then 100mm


well, i guess you know, is all about tolerances, repetablity expected / desired tolerance, and crafting it with low costs

---

one more thing : when you raise a part from the vmc table, you lose rigidity, and you won't be able to machine it at identical specs; if the part will be on that 4th axis tombstone, it won't be like it is securely in a vice on the table, so you shave time with less human/operator intervention between setups, but you lose time with lower specs

so, if you wish for your tombstone to be more rigid, check this tips :
... change aluminium to cast steel ( vibration dampening )
... make it shorter ( less buckling )
... make it thicker ( so put more parts around it's circumference, not across it's length )
* secure it nice to the 4th axis, because, in the end, is all about the rigidity of the 4th axis

can you share the part that you are machining now, and your actual fixtures, for each setup ? who knows, maybe someone will have a nice idea

i hope you find it usefull / kindly

Thanks! All useful advice. I've been thinking about how to address a lot of what you mentioned, like repeatability when removing the 4th and tail stock. I would like to have some kind of sub plate on my mill table with reamed holes to locate the 4th, the tail stock, and also a couple flat fixture plates I will need using dowel pins. As you said, the plan would be to get the tombstone mounted up slightly oversized and do all finish facing while mounted so the faces are perfectly flat with x/y travel. The lost rigidity is also something I considered. Since the parts still need 1 more setup, I can start on a flat fixture plate and do most of the roughing, heavy machining, then move to the tombstone to finish the last face, edge drilling and side features which wont be very demanding with rigidity.

I looked a little harder last night and found a couple videos of something similar. One of them was a haas doing basically exactly what I want to, but much bigger. Had a tombstone mounted on a beefy 4th with a bearing support at the other end. Seems like a pretty efficient way to do things as long as the strengths and weaknesses are considered. Do the heavy machining with first setup with rigid holding, then move to tombstone for lighter finishing and index work. 2 setups total when it would normally take 4.

[deadlykitten]

hello quinn

I would like to have some kind of sub plate on my mill table with reamed holes to locate the 4th, the tail stock, and also a couple flat fixture plates I will need using dowel pins

it sounds nice for reperability, but you lose rigidity; also, it seems repetable, but is not so repetable, because you will have play between the reamed holes and whatever goes inside them , and other things; of course, it will work, but hmm

4th should go directly on the vmc table, with strong ( big section ) clamps

you may replace the tailstock with a more rigid stuff ... i will do a little drawing ( oau, it looks dirty )

when you clamp all these, put the calibration axle on the 4th axis, check it's tir, then bring the 2nd suport, slide it on the calibration axle, and tighten all screws

that calibration axle, maybe will go inside the bore of your 4th axis ?

in the end, remove the calibration axle, and put the tombstone

the 2nd suport should have a sliding capability, and a pressure bearing, and maybe an open housing ( see atached ) and you tighten it; if you wish, i can deliver you a sketh, so to have an idea ( this suport should have a bearing that suports the tombstone, and it should also be able to be tightened in such a manner, that it will tend to compress the tombstone, so a 2nd bearing, pressure, is needed )

idea is to replace the tailstock with something more rigid, and put all those fast on the vmc table, but without losing precision; like this, they will be coaxial; if they won't be paralel to X axis, rotate your program, or rotate the entire ansamble before tigheting the screws / kindly

[QuinnSjoblom]

hello quinn



it sounds nice for reperability, but you lose rigidity; also, it seems repetable, but is not so repetable, because you will have play between the reamed holes and whatever goes inside them , and other things; of course, it will work, but hmm

4th should go directly on the vmc table, with strong ( big section ) clamps

you may replace the tailstock with a more rigid stuff ... i will do a little drawing ( oau, it looks dirty )

when you clamp all these, put the calibration axle on the 4th axis, check it's tir, then bring the 2nd suport, slide it on the calibration axle, and tighten all screws

that calibration axle, maybe will go inside the bore of your 4th axis ?

in the end, remove the calibration axle, and put the tombstone

the 2nd suport should have a sliding capability, and a pressure bearing, and maybe an open housing ( see atached ) and you tighten it; if you wish, i can deliver you a sketh, so to have an idea ( this suport should have a bearing that suports the tombstone, and it should also be able to be tightened in such a manner, that it will tend to compress the tombstone, so a 2nd bearing, pressure, is needed )

idea is to replace the tailstock with something more rigid, and put all those fast on the vmc table, but without losing precision; like this, they will be coaxial; if they won't be paralel to X axis, rotate your program, or rotate the entire ansamble before tigheting the screws / kindly

Thanks for the suggestions! I think it might be possible that I could have enough room if I leave the 4th axis always mounted and just have the tail stock removable to make room for other stuff like my flat fixture plates. I think that would be best if I was able to avoid taking down the 4th every time I need space.
Yes, you're right about the reamed holes/dowel pins. With a slip fit hole/pin, you're gonna have probably almost a thou of slop there, so I won't rely on that for positioning my 4th, if I can I'll just leave it mounted at all times. I'm curious though, if I want quick swapping of fixture plates without probing, is there a better option than holes/pins? Preferably something I can machine myself? Is there any cheap solution with very good repeatability? I would like to have accurate positioning within .01mm. Do i just need to always probe for that kind of accuracy? I've seen some fancy locators for fixture plates, like ball bearings that expand outward in a hole to center perfectly, but that type of stuff isn't really within my price range.

[rcs60]

haas does sell the option for doing what you are asking
4.5 x 4.5 x 20 inches tombstone
they also sell a quick change for the rotary table which is pretty quick on the change over

where i work we use the tombstone as a fixturing base with jergens ball locks. these are custom made for us
It can make going from one set up to an other very quick
with presetting tools you can start machining the first pcs.within 15 minutes of the last job

[deadlykitten]

if I leave the 4th axis always mounted

hello again quinn

is ok to have the load spread uniform across the vmc table, especially for setups / fixtures that are going to stay there for a while

for example, if the table can take a piece of 1500kg max, this part should have the mass center near the table center

a rotary is not so heavy, but keeping it on the side of the machine, will tend to rotate/lift the table, one guide way will be compressed, and the other will tend to lift; of course, depends on guide ways geometrical position ( orientation ), etc; maybe it does not seem much, but is like that advice that tells to remove unecesary stuff from a vehicle, so to reduce fuel waste

With a slip fit hole/pin, you're gonna have probably almost a thou of slop there

even if the parts are all nice, in tolerances, etc, those holes have to be large enough, so not to be affected by the rotary mass + thumbstone, etc ... too many variables

I think that would be best if I was able to avoid taking down the 4th every time I need space

do you use a crane, or something ?

if I want quick swapping of fixture plates without probing, is there a better option than holes/pins?

put on their back a rectangular prism, that is grinded, and that prism will go inside the T on the table, with small play; does it make sense ? check attached

like this, you achieave repetability on Y ( <0.05, depending on your T condition ); on X you can slide it, or block it somehow

after this, secure it with your clamps, and you are ready to go; you have full rigidity, since it is directly on the table

pls stop quoting my entire posts; i don't like it, i am just a human bean i suppose

they also sell a quick change for the rotary table which is pretty quick on the change over

hy rcs, please, is there a video or something ? kindly

[rcs60]

this is haas's video on there rotary option

Get More Productive with Haas' Rotary Accessories - Ask ... - YouTube

[deadlykitten]

nice video

that A frame only deals ( somehow ) with Z- and Y efforts; a tailstock will deal also with X- efforts, and full ZY

that "thing" that i was trying to describe at post #5, is a combination of both, thus, it is something like an A frame, made of 2 parts; 1st part is clamped on the table, while the 2nd one can slide, so to push just like a tailstock, but also have large contact area with the tombstone, just like the frame from the video

if the vmc is bt50, and you put on it a tombstone & 4th axis, then you can consider that you are machining with bt40 or bt30

yup, less operator time, but also lower specs; however, just saing, whatever works for your parts

of course, everyone wants to achieve a quick change time, and also high specs, and on a vmc it can be done, but it requires a bit more ( time & money ) than crafting a tombstone; well, easy steps / kindly

[rcs60]

the tail stocks that i use are the A frame type on a pallet that is about 20" long and one of them is the haas on a vf2ss
the demo from the Haas video is there quick change system that you were asking about and would not be as quick if you had to move the tailstock each time.
in the video they also only show the short pallet and not the 20" long tombstone where you would need more support at the end of the tombstone
this just makes for a good video to sell there system and you are correct that you will machine at a lesser MMR than if the part is directly fixtured to the table of the machine
but most likely the parts being machined are going to be smaller less machining done to them. this put more parts on the table,be able to machine on up to 4 sides of the parts and keep the spindle cutting longer and possibly being machined complete instead of having multiple operations that might cause problems from having these multiple op's and lets the operators handle more than a single machine
It all comes down to what is being machined and is it a good fit for machining on the tombstone?
all aspects of machining must be considered when doing any job even the machine tool that you want it to go on

[deadlykitten]

hy rcs, yup, true

hey quin, you still arround ?

if I want quick swapping of fixture plates without probing, is there a better option than holes/pins?

i just saw attached image today, in a video, and what i see is a part that is too raised from the table

i also remembered your question about quick swapping, and, for example, if you use those rectangular prisms, so to guide the fixture inside the T slot, you will still need to clamp it

also, that part from that image, may be put directly on the table, and, again, you need to clamp it

you may use automatic clamps, air/oil, etc ... craft some pistons, make them also rotate, find an hydraulic unit, or use compressed air, buy some hoses & distributors ( it costs less then how much i waste ), and you are done

some videos, to inspire you / kindly