cutting small diameter tubing accurately

Hi All:
Recently there was a thread on here that I can't find anymore about cutting hypodermic tubing to length.
Well it just so happens I have 5.5 mm long standoffs to cut from brass tubing 2 MM OD and 1.25 MM ID that need to be accurate within a couple of tenths.
I remembered that thread and thought I'd post a couple of pix about how I do it on the wire EDM so if someone else confronts this kind of problem they can see a potential solution they could choose if they want to.

So here they are.

The jig is a chunk of Ti6Al4V titanium, chosen because it's springy.
I cut the pattern you see into it and then pushed in the rough cut tube stock.
The tubing bores in the jig are 0.0003" undersize and the Tee shaped relief slots make it easy to push the tubes in but still hold them very well.

The jig was flipped 90 degrees in the vise and the one tube end was faced with the wire, then a slot was cut and skimmed at the other end, bringing the tubes to length within a tenth.
It cuts three at a time and I have twelve to cut.
The jig took a couple of hours to program and cut; 3 standoffs take about 5 minutes to rough and skim, so a total of 2 1/2 hours for the job .

Attached also is a couple of pictures of the assembly with the standoffs and the bearings in place.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi again All:
Found it...here is the original thread:

Cutting .026" Diameter 304SS to Length

Super solution. I can only dream about stuff like that.

man, you have enormous hands!

Your work with the miniature stuff continues to amaze me.

Nice work Marcus, but for 3 pcs. Seems like about a half hour of chucking them in a Foredom flex shaft and spinning against a stone would get you there +- .0002? Not as “techie” a solution tho, granted!

Good morning cyanidekid:
Actually there are a couple of other reasons why I chose this method.
First, I have 12 parts to make, not 3 so the investment in the jig is more justifyable.

Second, I did not know the actual length they have to be.
They sit both ends in a pair of counterbores so they function as locating dowels as well as standoffs.
I milled the counterbores on the Minimill with a cutter that had been touched off to a common datum with the reference faces I made the C'bore depth to, so I know approximately how deep they are but not to within a tenth.

If you get a chance to look at the thread where I posted about making the aluminum parts you will see how I put the halves together
after machining those standoff seats
I cut the bearing bores while the halves were still together as a single assembly and then cut off the bits I wanted to keep.
Here it is:
Some more cool tiny parts

When I did that boring operation I gauged the width of the slot between the halves.
My aim was to get the slot width with the standoffs in place exactly as it was when the bearing seats were bored.

So I cut a set of standoffs to the length I measured and calculated to be right and assembled the parts.
I gauged the slot again with gauge blocks, tossed out the almost-correct standoffs and cut new ones to the length needed to get the slot width right again.

It's a dirty cheater method to eliminate the consequences of tolerance stackup and to eliminate endless fucking around with the tenths indicator, the drop stand and the calculator...nobody cares if the bearings are centered perfectly between the cheeks, and nobody even cares if the bearing bores are perfectly coaxial but everyone cares a lot if they are either floppy in the bores or squashed oval by the cheeks, so I could be a bit cavalier about how I tackled this so long as I didn't fuck up those critical constraints.

I have no drawings, no dimensions, no tolerances for this build, but I need to efficiently make a prototype that works, and I need to be able to interrogate what I did so the production design with all its dimensions and tolerances can flow from all we learn from the prototype.

So yeah, if it was three parts only and if those other factors you were unaware of didn't apply, it would be reasonable to ask...2 1/2 hours to cut three tubes?..Marcus, you're fucking nuts!
As it was, this was still the easiest way for me to get where I wanted to go, and the customer is cool with how much it costs, so everyone is still smiling.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Neat solution to getting 3 pcs in a hurry at minimal cost. With my high production set up the change over would have take almost as long. We held things within .0005, so doing a dozen would have gotten 3 within .0002". Going back and forth on specs, price,and delivery would have taken even more time.
It is a winner!