I'm curious, what do most people do when they send parts out for a secondary operation and they come back wrecked.

I've got some reasonably tight tolerence 6061 T6 parts that I send out to have ground flat and paralell and then sent off for type 3 (hard coat) anodizing. Ideally I'd like to hold +/- 0.0002" on the thickness but I can accept a bit less on the overall dimensions of say +/-0.0005" as long as the sides are flat and paralell. the parts aren't huge being about 6" x 22" x 1.75" thick and made from 6061 T6.

I've made up plates and tooling to allow the grinder to clamp several parts in one setup to their table. Typically I send them to grinding and have them grind to 0.001" per side less than my finished needs since they will grow .001 per side in hard coating. If they grind a bit less off it still works out, but it's pretty had to build up over .001" per side.

So now the grinder has a less experienced operator grind a load of parts and misreads the micrometer and makes 11 of the parts 0.005" to small.

My options are limited to:
- Remake the parts- Although it's really time consuming to set up all the operations to remake just 11 parts.
- Try to weld repair the parts, face them off, regrind them and hope they anodize equally... I'm not sure it can even work
- Try to convince my customer that nickel plating is a viable option. I'm pretty sure I can grow the plating far enough, although I'm not sure how flat and paralell the parts will become, or how well nickel plate would stand up compared to type 3 anodizing.

I'm kind of hoping someone here has a better idea. Who pays for the grinders error typically? I realize stuff happens, and either way I have to make it work for my customers in the end.

Curiously,

Stu

He does, for the entire re-work to the stage where it goes for grinding,

My advice would be NOT in anyway shape or form to weld or build up the surface WITHOUT, I repeat WITHOUT written instruction from your customer.

If you f'd up the grinders work you'd have to pay.

Letting him get away with it will only encourage others.

''making it work for your customer'' is a red herring,

I specialize in welding and I would not recommend welding these parts, the amount of energy absorbed by the material for Al of that size and thickness will cause the material to lose its temper, even if you send it out for treating post welding and than re machine the parts you might find issues with the anodizing after grinding.

Stu,

I can understand your desire to be a nice guy, I'm guilty of it all the time. But there's no reason that the grinding shop shouldn't pay for your time and materials to fix their mistake - by starting from scratch if needed. That is, unless you have made an agreement that sates otherwise in the fine print.

Lets look at it this way.
Who pays for the parts you scrap?.....
You do.
The grinder should pay for the parts they scrap the same as you pay for the pay for the parts you scrap. Whether you charge them any extra for the PITA factor, is up to you.

"So now the grinder has a less experienced operator grind a load of parts and misreads the micrometer and makes 11 of the parts 0.005" to small."

If you know this as fact, then the grinder pays the tab.

Simple.

How are they gonna remember next time unless it hurts this time?

Ditto to above replies on "who pays."
I can also tell you, you will have anodizing issues if you tried to weld them up.
It will show up like a sore thumb.

Plus, welding over anodizing is a disaster -- it's an oxide (which is what shielding gas tries to prevent) and you'd have to mill off a bunch of it to get under the penetrated anodize, and even then, you would get contamination from the sides.

I do some plats that need ground and then anodized. Lots of holes in them and tight tolerances. Here is how i do it (for the future)

Have the grinding shop buy material then grind them for you to print. Then you machine them and hope the anodizer doesnt screw them up. This takes one possible issue out (grinding) but you may have to pay just a little more for it. If the grinder scraps material he purchased you arent out anything.

In a perfect world the one screwing up the part should pay for every one elses time/materials before the mess up.

Typically I do the same thing, only I supply the blank parts, have them ground to size, and then I finish machining them. If they get screwed up I try to minimize my exposure to as early along the process as possible. In this case my customer was short on time and had some existing parts that were .080" oversized in thickness, but otherwise already had the profiles and internal coolant passages and ports all completed. I simply had to have the existing anodizing removed, machine the sides to the appropriatte dimensions then send out the parts to be finish ground then anodized.

So now I need to bring in new stock and start from square 1 which will greatly add to my costs, and delay the customers final delivery of parts... sigh...

Even if the grinder does a perfect job, the anodizers still have a great opportunity to screw things up as well, so there is no way to eliminate all the risks.

Actually there might be.... I once had to do some very expensive end caps machined from billet titanium 16" thick x 86" in diameter. I found an insurance policy to insure the job if it didn't work out. It was VERY expensive but required since I coluldn't afford to eat the part if we screwed up. I wonder if there is a smaller policy that can be purchased to include screw up by outside vendors...

In our area if the grinding shop screws up they have to replace the parts and grind them again.

The grind house eats the cost up to the point they started on them (labor and material is fair).

Do not try to build up a surface this large with weld. It will be a piece of junk and look terable after anodize. It would also require re-heat treating to get into -T6 condition.

I wouldn't ask for a pass on the quality to my customer because of one of my vendors mistakes. Give your customer what they asked for and every one is happy, except for the "new guy" who made the mistake. If something were to go wrong with your work around or repair that you stand to eat the job down the road if you rework idea fails. Would the chrome chip or oxidize or anything that would displease your customer? Do you know all the atmospheres the parts will be used in? It wouldn't be worth it to me to gamble.

I agree with most of the above posts, BUT, I would not be surprised if the grind shop refuses to do any more parts. If I understand correctly, they usually just grind blanks, but in this case they were accomodating you by grinding almost-finished parts.

I often get requests to do just a one or 2 hour EDM or grind job on a high-dollar part. I look at the risk vs reward of each job and sometimes turn them away.

Perhaps meet the grinding vendor halfway, if you still want to keep a relationship with them?

I just went down this road a week ago. A rather expensive tap spindle we had finished was scrapped at the grinder. They replaced it. Not only did I have time into it, but it also had been sent out to have a spline cut, some internal broaching and heat treat (including straightening). The cost of that screw up was big, I assure you. They had several times the original amount billed for the grinding to cover replacing that spindle.





Frank



www.randolphmach.com

This is a risk you took when you sub the job to outside party. When we do job works of customer's parts, if we screw up the part, the SOP is not to charge for the replacement part. No one likes to screw up your part, talk to the vendor, redo the part asap, and he will support you by completing your replacement part asap, free of charge. Asking him to bear the full cost is too much. Next time will he dare to touch your job? I know it is painfull.

IMHO

www.titanengg.com.sg

Over here we think different, if you cant grind yourself and have to sub out, and the grinder screws up, you dont have to pay for that batch, and the next.
If they keep messing up we learn about their standards and move on, but we tell them.

If they offer to cover all costs, and promise/show improvement we try again.

But another question, do you have a % of production loss, 1 or 2 % is normal in a high quality machining environment, do they reach that 1 % taken over a year?
If they do, then take it easy on them.

22" x 6" x 1.75" +/- 0.0002 or 0.0005 on something anodized ?
Is he grinding the whole surface or just a few lands ?
It seems like breathing on this thing will warp it.

I'm amazed the grinder took this job...with your tooling... and no agreement on who pays for screw ups.

Am I missing something ?
Give us some more details.

SM

Actually it's a fairly simple grinding job, but the parts have quite a bit of work into them by the time they are ground. The only real cahllenge is the parts are about 1.75" thick x 6" x 20" and they are 6061 aluminum, so they obviously can't be gripped by the magnet on the grinder alone. Rather than simply block the parts in, we supplied the grinder with several steel plates that are large enough to secure the aluminum parts. The parts are retained through a substantial internal groove and some tight fitting spuds. In use the steel plates are ground on 1 side, flipped and ground flat and paralell on the other side, then 2 parts are stacked back to back on the fixture so they can't rotate. They are secured to the fixture solidly with a bolt and a spud. the parts are then ground so the upper surface is flat, then flipped over to grind the other side paralell to the first side, and to a specific thickness.

I left a properly ground guide made to the same dimensions so the grinder can have something to measure against as a standard.

So how tough is that supposed to be to get a part flat and paralell within .0002". Breathing on it certainly won't warp the part. I've had them ground before and easilly hit .0001". On a run of 30 guides, they were all within 0.0002". Clearly it can be done if a grinder exhibits reasonable care, grinds the mounting surfaces before mounting the parts, and keeps the parts and fixture clean when you grind in the second side. I'd say grinding the parts .006" to thin is more than a little bit of an oops. there was no way to salvage the parts, and they were scrapped.

Maybe I'm expecting too much. What do you think?

Curiously,

Stu

They had a new operator, and THEY should have watched/checked him closer.

Just remake them and tell the grinders what it is going to cost. Welding will warp, and even with 5053 rod that will anodize, look different.

It will stand out like a turd in a punch bowl.


JAckal