Water Jet Cut Holes 1

[BUGGAR]

I've been fabricating prototypes with water jet cut plates. I have been specifying holes to be drilled to the usual drilling tolerances. A water jet shop suggests water jet cutting the holes and then reaming them to size - it is substantially cheaper.
Does anybody have experience with water jet cutting holes 0.250" and 0.375" diameters in 1" thick 6061 T651 plate?
Thanks.

 

[SwinnyGG]

1" AL plate should be no problem for an experienced water jet operator.

If your parts will be produced with lower cost, what is your concern?

 

[btrueblood]

There might be a significant taper in a 1" deep hole (several thousandths of an inch).

 

[MintJulep]

Cheaper than what?

On the face of things, if someone offered me reamed holes + a refund vs a drilled or jetted hole I'd take it.

But makes me wonder. If we guess that the holes are jetted to a rough size, then reamed by a "CNC" secondary operation then there are two operations.

If you are ok with drilled then why not drill? One operation. Maybe your parts will get even cheaper.

 

[rb1957]

I thought the same (if reaming why not drilling). maybe time to drill through 1" thk plate ??

and if the contractor is set up to do the two operations, it may be cheaper. If (for example) he had to send out to a water-jet shop and then ream in house ... hard to see that being cheaper.

Do you need a reamed hole, or is that what he's offering (to clean up his water jetted holes)?

another day in paradise, or is paradise one day closer ?

 

[TimSchrader2]

If the Hole or holes needs to be located more precisly than plus or minus .008 we will usually drill it. And there is a taper as mentioned above. The Wjet people here charge extra for a tolerance that is closer then .008. We do often ream the holes later in a Wjet hole when we can. Maybe the newer Wjets are better.

Done quite a few of 1" thick alum and more. But the hole sizes are generally 1" or more.


Wjet is much cleaner and less tapers than the plasma machine we have.

 

[EngineerTex]

It seems like nobody here has done the waterjet in that thickness of aluminum. (Nor have I). I presume that your original post is a question to see if anyone else has had problems/pitfalls with this particular procedure for small holes in thick plate. I also presume that your question only arises because you don't really care how the holes get there, just that they get there, i.e., "Hi, Mr. Hole-Punching Contractor, here is my part, put holes in it please," and then you don't really care if it's some alien technology that puts the holes in there, as long as your part is returned perforated.

In that sense, I have never had any problems with using water jet and having extremely tight precision, but this particular case (small hole in thick plate) may require you to send a scrap piece and have them put a dozen holes in it with their process to verify quality. The only experience I have with water jet is that at the original penetration, (the bottom of the hole at the start of the cut), it is much wider than the kerf. Note that the bottom blowout is much smaller than 0.25", but that was also on thinner material. If they say it should be no problem, then it probably isn't a problem, but I would definitely get a sample piece done, in order to make sure that their salesman isn't making promises that can't be kept.

Engineering is not the science behind building. It is the science behind not building.

 

[BUGGAR]

Thank you all for the input. Here’s what I’ve learned so far:

I had them make up a part from 0.75 inch thick aluminum plate with holes and slots. I specified Q3, Medium Smooth cut surface finish which seems to be the standard finish with local shops.

There was no problem cutting the 0.25 and 0.375 inch diameter holes or the 0.375 by 2 inch slots. The hole surface was “fuzzy” and my high school shop teacher would give me a D for these, but their X-Y positioning was perfect. Taper was not measurable, mostly due to surface roughness. The diameters of the 0.25 and 0.375 holes measured, average between bumps, at 0.30 and 0.40 inch respectively. We use high strength bolts (12 pt and socket head) and they fill the holes O.K. The holes had been reamed (drilled) to clean them up so there were no tights. Actually the holes are perfect for our prototyping with just enough tolerance for assembly. But I wouldn’t want a client to look into one.

The big saver on waterjetting is in the slots. We had to have these milled previously.

Thanks again.

 

[Sparweb]

Having dealt with WJ parts for years I am still not impressed. The surface quality is terrible without another cutting tool going through it (whether that's a drill, a reamer, or an end-mill). We accepted it on some prototypes several times, including many aluminum parts (up to 2" thick). But any time we wanted to bring the parts to production quality (aerospace) there was no way to justify WJ because the clean-up took just as long as placing the stock on a milling machine and doing the whole thing there. Couldn't even use it for tooling because the accuracy isn't there.

Admittedly, we make parts where fatigue, corrosion, load distribution, and the consequences of failure are concerns that must be actively prevented. If you're making parts that can remain in service even when corrosion or cracks are found, then, yeah, whatever...

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[BUGGAR]

SparWeb, I totally agree with your words.

ps: the parts are for off road racers and we break a lot of prototypes before we decide on which part goes into production made "the right way". Right now we need cheap parts to break out in the desert to see what works. I love my job!

 

[Sparweb]

Yup, building your own toys is almost as much fun as BREAKING your own toys! Why is that??

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[tbuelna]

The diameters of the 0.25 and 0.375 holes measured, average between bumps, at 0.30 and 0.40 inch respectively.

Reamers are only intended to remove very small amounts of material from the ID surface of a hole already machined cylindrical and just slightly undersize. As others noted, if you have to set the plate up to finish ream the holes to close tolerances, it should not cost much more to start by drilling those .25/.375 dia holes in the same set up. Plus, by drilling you'll get the benefit of more precise positional location of the holes, and less wear/tear on your reamers.

 

[berkshire]

One thing to watch on water jet cut parts, is that a lot of water jetters use Garnet as an abrasive media.
When I was working for a living, we had several hundred parts made, with a certain hole, piloted in, to be drilled out to size later.
We noticed holes getting undersized. When we investigated, we discovered that the dust on the parts was actually pulverized media ( Garnet.), and it was wearing the drill bits.
After we started pressure washing the parts, before we drilled them the problem went away.
B.E.

You are judged not by what you know, but by what you can do.

 

[3DDave]

B.E. - how long did it take to realize those were the shiniest bits they had ever seen?

 

[BUGGAR]

berkshire, that was a good point. Wire brushing exterior cut surfaces of similar steel parts seemed to create more of a "powder" than I would have expected. The aluminum cut surfaces are matte grey and I will explore them today. I have to find out what abrasive they use. There also seems to be a lot of variation in quality between different machines and operators. This is like welding.

 

[MikeHalloran]

As a point of reference, a former shop used to drill a 1.5" dia. hole through 2" 2024-T4 aluminum in six seconds, using a carbide spade drill in a CNC mill, with no pilot hole, with a really nice finish, suitable for a binocular load cell.

According to my calculations, verified by real time load meters,
the operation loaded the 10HP spindle motors to 13.5HP, which was allowed for a short time per the machine's documentation.

The fun part for me was watching the (short, perfect) chips fly up and bounce off the high ceiling.
Of course, I didn't have to sweep the wet chips off the floor.





Mike Halloran
Pembroke Pines, FL, USA

 

[IFRs]

Waterjet is perfect for many operations. Tight tolerance holes with accurately located centers is not one of them. Note: a better finish is usually the result of slower travel speed, which is more expensive...

 

[BUGGAR]

Mike,
After seeing the youtube video, I had to try a wood spade bit in a cheap drill press. It sort of worked. I got a three quarter hole in a three quarter T651 plate but it was peck and lift, peck and lift all the way. The chips were barely foil thick but showed a nice shear pattern. No chatter. It took forever but the hole was beautiful. And the motor HOT.

 

[EngineerTex]

Uhmm... I don't think he meant a wood spade bit... Though I did have to watch the YouTube video and I'll imagine it sure did get hot.

https://www.drillbitwarehouse.com/store/c/solid-carbide-spade-drills

Engineering is not the science behind building. It is the science behind not building.