Turning large stainless steel plate

igor2610 · Oct 31, 2019

Hello everybody. My first post and first large part on new machine.
Machine is CNC VTL with C axis and live tooling. Table diameter is 1600mm(63in) with 4 independent jaws and t-slots.
Part is 1.4404 stainless steel plate 1195mm(47.04in) in diameter, 18mm(0.708in) thick with 359mm(14.13in) hole. Raw stock is 20mm thick plate cuted with water so I only have 2mm(0.079in) allowance on thickness. There is some allowance on OD and ID.
Tolerance on flatness and paralelism is 0.3mm(0.0118in).
On OD I need to turn 20 degree taper 15.5mm(0.61in) long.
There are also some holes and face grooves on one side.
How do I approach this job? What to do and what to avoid? Clamping, setup?
Im operating this machine for couple months and before this I worked on CNC lathe with 12in chuck so this is pretty different and chalenging.

bryan_machine · Nov 1, 2019

1. Please be very careful handling parts that size.
2. On instagram there's a guy tagged heavyironchris who seems to have a business running large VTLs, and some of his videos show setting up pieces not unlike what you describe.
Chris Moore (@heavyironchris) • Instagram photos and videos
He is using mostly manual machines, but the setup procedures should be largely the same.
(You'll have to scroll through the instagram account and snoop around - but there are examples in there were he sets up large parts with similar constraints as yours.)

[None of the usual youtube suspects seem to do much with VTLs....]

I've never run a VTL, but it does seem (from videos noted above) that a key thing is setting it up like one might a regular 4-jaw on a lathe - right down to running it around past an indicator and loosening/tightening opposite jaws (with a rather large wrench) to center up.

McClure Machine · Nov 1, 2019

igor2610 said:
Hello everybody. My first post and first large part on new machine.
Machine is CNC VTL with C axis and live tooling. Table diameter is 1600mm(63in) with 4 independent jaws and t-slots.
Part is 1.4404 stainless steel plate 1195mm(47.04in) in diameter, 18mm(0.708in) thick with 359mm(14.13in) hole. Raw stock is 20mm thick plate cuted with water so I only have 2mm(0.079in) allowance on thickness. There is some allowance on OD and ID.
Tolerance on flatness and paralelism is 0.3mm(0.0118in).
On OD I need to turn 20 degree taper 15.5mm(0.61in) long.
There are also some holes and face grooves on one side.
How do I approach this job? What to do and what to avoid? Clamping, setup?
Im operating this machine for couple months and before this I worked on CNC lathe with 12in chuck so this is pretty different and chalenging.

Are all the holes etc put into the plate before surfacing or after?
I have a number of rings and blocks that match the jaw step hight to support the middle of the part. If you try to just hold the outside it is going to chatter and ring like a bell. I would probably surface, then bore center hole, clamp through the center hole. Then cut your grooves, and bore your holes, then clamp part through the drilled holes and center, remove the outer clamp jaws and finish od.
A 50+ " boring mill vtl is not a toy, I am guessing 50-75hp, when you think it's clamped enough double the clamps. If you have enough waste on the outside it's a good idea to weld a few stops on the part and slide stop blocks against those, just in case something grabs. I had a 11000 lbs part shift on a 120" vtl it will get your blood pumping trying to get to the estop.
When you are surfacing, make sure you come down a few thousand then back up to size to remove backlash. I have seen quite a few parts undersize from not doing this.
Just go slow and think about what you are doing before you do it. You will be fine
Good luck
Mike

g-coder05 · Nov 1, 2019

When I do big VTL work I try to get the ID first and will weld points to put shackles and turnbuckles on to make sure she stays in place. This is a picture of a nuclear waist transport container I used to make that had to get about 3" bored out. I had extra clamp points on the bottom and loops at the top. Never had a problem. VTL's are the most dangerous machines in a shop, At least for me since I got hung in one and took a mad hatters wild ride. Take your time and don't skimp on the setup.

litlerob1 · Nov 1, 2019

A variation of what g-coder posted..first priority is getting a surface worthy of holding. Slow and easy to get a Machined surface, re-orient it and you can get a little braver. But if people are quoting Vertical Turn jobs as time crunch profitability, they are fucked out of the gate. That's not how you make money on a VTL.

R

igor2610 · Nov 2, 2019

Thank you all for your replys. I started with part today, just faced both sides. It came stress relieved, but again after facing it warped( which is probably expected), so my foreman suggested that we stress relive it again.
I didnt saw your answers until now, so i clamped it like this:
just rest the part on machine table, and clamped it lightly at 6 points with these type of clamps

Faced it from bore toward OD with light cuts and didnt have problem(except warping). I have litlle over 1mm(0.0393in) left on thickness so im not sure that is enough to clean both faces and achieve flatness and parallelism, but i will deal with that when part comes from relieving.

litlerob1 · Nov 2, 2019

Work on Perpendicularity from the Face to the OD. I'm guessing you are over tightening your clamps.

igor2610 · Nov 3, 2019

litlerob1 said:
Work on Perpendicularity from the Face to the OD. I'm guessing you are over tightening your clamps.

You mean that I machine Face and OD in same setup.I didn't think it matter but I'll try that. It is little hard because clamps and part are almost same height so I have to put some thin blocks in beeween.
Also i will try to clamp with less pressure, but it's little tricky because I tighten it with hand and I'm afraid of part flyin out.
Maybe it's not warping from over tightening, maybe it's just the way Stainless plate behave when you face them. Guys in shop who work on milling machines and who machined bigger plates say it's normal for them to warp and that you have to machine both faces couple times to get it flat and parallel.

litlerob1 · Nov 3, 2019

I explained myself poorly. Clamp the fuck out of the raw material. Work on Perpendicularity from the Face to the OD, in a single operation. Flip the part over, then you have surfaces to clamp on. Perpendicularly in the first operation, for Turning jobs is a fundamental way to improve everything else. Consider a very round part that is extremely out of Perp. most wouldn't even think twice to make it right. Same principle, on a more accurate scale.

R

mountie · Nov 4, 2019

igor2610 said:
Thank you all for your replys. I started with part today, just faced both sides. It came stress relieved, but again after facing it warped( which is probably expected), so my foreman suggested that we stress relive it again.

A little late for this job, but in the future you may consider having the part Blanchard ground.

igor2610 · Nov 4, 2019

litlerob1 said:
I explained myself poorly. Clamp the fuck out of the raw material. Work on Perpendicularity from the Face to the OD, in a single operation. Flip the part over, then you have surfaces to clamp on. Perpendicularly in the first operation, for Turning jobs is a fundamental way to improve everything else. Consider a very round part that is extremely out of Perp. most wouldn't even think twice to make it right. Same principle, on a more accurate scale.

R

I get it, gonna try it when part comes. Just afraid it will deform after I release it if clamped hard or it doesn't matter for first Op as long as Face and OD are perpendicular( will they be if Face which is large surface bends). I have just little over 1mm stock left on length, so not much room for playing.

igor2610 · Nov 4, 2019

mountie said:
A little late for this job, but in the future you may consider having the part Blanchard ground.

That is not an option, we don't have that kind of grinder or anyone near us.

igor2610 · Nov 5, 2019

McClure Machine said:
Are all the holes etc put into the plate before surfacing or after?
I have a number of rings and blocks that match the jaw step hight to support the middle of the part. If you try to just hold the outside it is going to chatter and ring like a bell. I would probably surface, then bore center hole, clamp through the center hole. Then cut your grooves, and bore your holes, then clamp part through the drilled holes and center, remove the outer clamp jaws and finish od.
A 50+ " boring mill vtl is not a toy, I am guessing 50-75hp, when you think it's clamped enough double the clamps. If you have enough waste on the outside it's a good idea to weld a few stops on the part and slide stop blocks against those, just in case something grabs. I had a 11000 lbs part shift on a 120" vtl it will get your blood pumping trying to get to the estop.
When you are surfacing, make sure you come down a few thousand then back up to size to remove backlash. I have seen quite a few parts undersize from not doing this.
Just go slow and think about what you are doing before you do it. You will be fine
Good luck
Mike

Sorry for late reply.
I didn't hold part with jaws, but with clamps as shown few posts before( don't know how do you call them, I have never used them before).
Part wasn't laying on blocks but directly on table.
Plan was that I first surface both faces to get Flatness and Paralelism, and thickness to size.
Then I plan to hold with toe clamps inside the bore to turn OD, then move clamps outside and bore ID, drill and tap holes, and turn axial grooves. I can't hold through holes, they are blind.
Am I making mistake holding it directly on table and not on blocks clamped with jaws?

Ox · Nov 5, 2019

If it was me - I would clamp on the ID first and face one side (big serrated jaws - or maybe just table clamps) and doo the OD.
I would NOT clamp it to the table, but maybe use s sort of "machinist jack" around it in several places to support it "where it wants to lay" and then face it.
Flip over and use smooth jaws on the OD and face and bore ID.

.012 flatness will be interesting on that thin of a plate, but maybe?
Just may need to flip it a cpl times and skim cut it.

----------------------------

Think Snow Eh!
Ox

igor2610 · Nov 5, 2019

I'm not shure that my jaws can get close enough to clamp on ID, I'l check it.
They are like this

T slots for jaws don't go all the way to center of table.
Also I don't have smooth jaws. I can use some aluminum shims between jaws and part, right?
On OD there's not lot of surface to hold onto, only 2.5mm(0.1 in), rest is 20 degree taper. I'm woried it won't be enough.
Yes, flatness is problematic, will we have benefit from stress relieving it couple times beetwen facing cuts, or is it waste of time.

Ox · Nov 5, 2019

I can't answer about the stress relief.
Does more than once help?

.100 should be sufficient if you had smooth jaws.
You don't have something soft that you can bore?

You don't need to grab on to too much - but preferably your .100 would be in the bottom of the jaw.....
You're not dooing much work at all, and you don't have a big mass sticking out in your Z, so it should take very little to hold on to it.

----------------------

Think Snow Eh!
Ox

igor2610 · Nov 5, 2019

We will see does it help to relieve it more than once. Raw stock came relieved but after facing both sides it wasn't flat. It will come from second relieving today.

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