milled lost tram while milling

[Henk]

It may be weird, but I like reading about the mishaps. That probably says a lot about me, so I thought that as a compensation I should at least do a write-up when it happened to me.

So I have watched the nice hex and square collet blocks for a while, and I wanted one as well. Though I did not want to spend the money for a full set of the associated collets. I decided to make one for the collets that I have (forgot the actual designation just now). It also means I can use the existing closing nut which is a bit too complicated for me (I hope it will not be in the future though).

Found a suitable size of mystery steel. Setting up the RT in horizontal position (first time for me) was not that complicated with a pointed pin in the vice. At least for the amount of use it would get, I am not going to buy a dedicated "tailstock" (I am not sure it is the right word - I suppose you understand what I mean) for it. Height was adjusted by moving left/ right with a DTI in the spindle.

Here I had just finished the hex part (rough, just needing a little shave to reduce surface roughness). I decided to make a 12 sided version so that I could choose between square and hex usage. This of course reduces the angular accuracy a bit, but I will mostly be using this thing for making hex screw heads - so no high accuracy needed.
I should have paid more attention however. I noticed that the cutter moved down by itself:

It can be seen by from the slight waviness of the edges. I tightened the collet even more, and went on.
Then minor mishap: cutter dug in by 0.5 mm. It was also clear now what happened:Mill head obviously just rotated.

Lesson learned: when it seems something is loose, it is. Make sure you find it!
Otherwise, I learned that I need to really tighten the head. I had noticed that the larger cutters (which is for me 12 mm or more) seemed to creep down, and now at least I know what it probably was.


By now the left hand side is too small by 1-2 mm to make the thread.I am not sure whether I will use this piece to do a trial run for the other operations (large external thread, internal taper matching the collet) as there is still ~20 mm length left with a large diameter. I still want to make this collet block, but it may take a while before I find the right size metal.

Henk

 

[sara736]

Looks good Gus, thanks for posting. This looks like what we call a "craft shop", do you ever go to a just a tool shop in Japan?

 

[gbritnell]

Hi Henk,
It's the old physics trick at work. The larger the diameter of cutter the more leverage it has. By this I mean the farther the cutting edge is out from the center line of the spindle the more leverage it has to twist or move things. When using a smaller mill a person has to know the limits of his machine and make adjustments. There are several things to keep in mind when milling. Always make conventional cuts (as opposed to climb cuts) when roughing stock. This will prevent the cutter from pulling the stock and therefore the looseness in the leadscrew and causing a problem. For finishing I always climb cut but on a loose mill you might want to snug up the gib lock screw a little bit to prevent it from pulling.
Rigidity is the keyword for any type of machining, whether it be on a mill or lathe.
gbritnell

 

[SmithDoor]

That happen with ever one using mills
I have only had one mill this did not happen with. The head was cast in to the base it built around 1910 best mill I ever had
The only way I ever stop this was just keep close eye and making a light finishing cut.

Dave

 

[bazmak]

Common problem.Ive had many misshaps.The cutter trys to screw itself into the job.either pulls the tool downthru the collet or takes up backlash or pulls the job up into the tool.I have tried using rotabroach cutters as end mills or facing.Very difficult.The cut just gets deeper.Use a pozilok collet.Tighten everything up solid.Still havent overcome the problem.The geometry of the rotabroach is such that it tends to pull into the work.Which is correct i suppose as the tool is designed to plunge cut and not face mill

 

[purpleknif]

Setting your Y axis by going down beyond your needed location and then coming up to where you need to be and then locking it in will go a long way towards solving this issue.

 

[jj-smith]

Setting your Y axis by going down beyond your needed location and then coming up to where you need to be and then locking it in will go a long way towards solving this issue.

Purpleknif,

I think that's excellent advice! I do it out of habit on the lathe as I have worn out ways on the compound.
I caught myself doing it without realizing on the mill to, and found later that forgetting to adjust the gib screws on different types of work will inadvertantly get you to the point of messing up a cut just before all the work is done!

Regards, J.