Milling, dumb bunny question...

[John Hill]

OK, I have had my mill for a few months and by rights I should be turning out all manner of wonderous stuff but in reality I have only used it for pretty simple jobs. 

Then I made my tangential tool holder which involved rotating the mill head to drill the 12 degree holes and of course then getting the mill back in tram.

Ordinary people would just reach up to the shelf and get their B&B** tram indicator and the job would be done in a thrice,  but not me, I used a set square as my DTI does not want to stay stuck to the quil.

Proof of the pudding, using a fly cutter (specially made for the occasion) ripping the scale of a bit of old angle iron I get the faintest cross hatching appearing on the work indicating I presume that the cutter is cutting full circle.

Is that really what I should be seeing?


**B&B  Bogs and Bandit, well known metal artisans from late in the Second Elizabethan era.

[Davo J]

Hi John,
You can use a bent piece of rod in a collet to mount the dial indicator on for now.
As for the cross hatch pattern it sounds like it turned out fine, that would mean the tram is out slightly which is good for the fly cutting.
You would find if you fed it from the other direction it would leave a different pattern with one side being deeper. 

Dave

[picclock]

Does this mean that if I deliberately introduce a tram error, and move the work in the error direction I will get a better finish?  Presumably this will cut deeper in the centre by the error amount leading to a slightly concave surface.

I'm looking to make some very fine finishes on some work and if this is the trick I'm up for it. I even ordered a carbide profiling tool for flycutting this job to get the best possible finish, and am currently working on a motorised x feed* for the same reason (and cos I'm lazy )

Best Regards

picclock

*scrap battery drill motor and gearbox with scrap angle grinder head final reduction stage 

[PekkaNF]

Jup, to my understanding the head is a minute amount inclined, this is some importance with carbide insert cutters. They are not big on rubbing (on the back stroke....)

No, there are two different distictions on here:
* Quality of the finish, ie smoothness
* Geometry: trueness, flantness you name it

They are little different, not although completely different.

Peeple like fly cutting, because that produces uniform finnish and on quite a few cases little concave part is easier to mount without rocking. But larger the cutter radius, bigger the effect of head/quil error is. You can see this if you face a surface with end mill may times over - it looks untidy, but when you blue it it does not look far off. Then again if you fly cut face on one go, it looks rather convincing, but it bears only on edges. How importat that is depends completely on your needs. THen one thing is spindle "float" - if th spindle bearings etc. are not rigid and only with minimal play cutting forces tend to "lift" the cutter, noticeable at the start and when you change cutting direction - adjustement, power feed and dicipline helps here. I try to cut to a most flattering direction when I can.

This is an advice of relatively unexperienced, threat it accordingly.
Pekka

[Bogstandard]

You can deliberately set your tram slightly out to give you a very smooth, in fact, mirror like finishes, purely by using the very tiny amount of back cut that you can get. But you must make sure, to get that sort of finish, your lead cut is no more than a couple of thou (0.05mm). The reason for that, if the lead cut is too deep, and both faces are on the cut surface at the one time, the normal flex obtained by taking a fairly heavy cut can push the back cut down more than you want, and when the lead cut comes off the job, you will be able to see where the back cut has lifted slightly, and so spoil the finish. On my production runs I used to use that little trick all the time, to get great finishes, as the amount of concave cut is almost negligible.

But here is another reason I didn't put my tram straight for flycutting but used a large endmill instead.

http://madmodder.net/index.php?topic=2083.msg22206#msg22206


Bogs

[John Hill]

Dave, good suggestion about the rod in the collet to hold a DTI, I knew I should have done that but I just reached for a set square instead.

Picclock, if I read these comments correctly, yes a good fly cut finish will be ever so slightly concave.

Pekka, thanks for the comments.

John, I need to get a bit more scrap metal to experiment with.  It seems fairly easy to get a good finish on a small piece but it is only the bigger bits that I can get to see all the issues with a +50mm diameter fly cutter.  I looked at your other topic (dont know how I missed it at the time!), very interesting.



John

[kvom]

I find that on my Bridgeport using a 123 block as a square on the spindle will get the tram square to within a few thousands.  Then a DI or DTI is fast to get it to within .0005 over 6" in both X and Y.

[Davo J]

I fly cut this piece of mild steel plate that is 220mm x 340mm last year for a job and snapped a few pictures. I used the boring head as it was quick and easy at the time rather than making a large fly cutter. It's a 75mm boring head with a 18mm bar that takes HSS and I was running it at 220rpm my slowest on the mill.
From memory I took around 0.5mm for a clean up, then another cut after resharpening at around 0.2mm. I soon found out the HSS needed plenty of coolant or it would loose the edge real quick.
The plate needed the 8 holes so I drilled them smaller so I could use socket head bolts to hold it down on the table.

Dave

[Miner]

One thing not mentioned that I could see. The larger the diameter of your flycutter is then the lighter the cut you want to make as the interupted cut tends to hammer the spindle bearings. Also check your magnetic D.I. base. Most times you can just unthread the post and insert that in a collet or drill chuck for tramming your table with the rest of the parts for the indicator.

Pete

[Pappy Frank]

Hi,
Dave mentioned using a piece of rod to hold your DTI. Early in my learning experience (close to 30 years ago now), I used to look through catalogs and make many of the tools I use today. One of the things I made was a set of holders for my indicator. I looked at the pictures and gathered up a fine pile of odd pieces of metal and went to work. I still use that set, and would not even think of buying a replacement. I have added to it through the years.

God Bless
Frank

[Bogstandard]

It seems that things are going backwards.

I showed how to make a much more and easier to use method of getting your tramming done, to get away from the swinging of a dti thru 180 degrees, where you need a rubber 12" neck to see what is going on.

http://madmodder.net/index.php?topic=822.0

The same system is now available for purchase if you don't fancy making one.


Bogs

[John Hill]

Not at all Mr Bogs, I fully remembered your tramming appliance and perhaps I will even make one one day, my question was to do with what the product of a properly trammed system should look like.

[Minutes later] Actually John I went back and read your topic again, third time at least, and I see that in the very first post you described what a properly trammed system should produce with a fly cutter...  I guess I should read things more carefully. mea culpa..

[Bogstandard]

Actually John,

When cutting non ferrous, it is rather rare for me to take the flycutter off the machine, because I use it not only for very fine finishes, but mass metal removal as well.

It is a grossly misunderstood tool, some people only thinking it is for getting fine finishes, but I have found with the correct shaped tool, it will do both deep and fine cuts with no problem, and sometimes it can get into areas you could only normally get a cutter in without resetting the setup.

In fact it is nothing for me to remove 0.100" (2.5mm) in a rough cut, then a couple of thou (0.05mm) to give a mirror finish, straight after each other.

But you must know the flexing limitation of your machine when using a flycutter. On something like yours, you can do depth of cut like I do, but say on an X2, you would be lucky to get any sort of decent cut using 1/5th of the rough cut I use.

I have shown the shape of the tool I use many times in the past, so I should not need to go thru it all again.


John

[picclock]

When using a flycutter for final surface finishing on a flat plate what is the best diameter to set the tool at ?

If I were to set the tool cutting edge at exactly the work width the tool would never leave the work and become unloaded thus giving a more even cutting pressure, however the cutter would go over the edge section far more that the middle section (as the edges of the cuts overlap).

If I were to set the tool at a much larger diameter although the cut would be interrupted the cut distance would be the same for all cuts but as the cut is interrupted the shock loading on the tool would almost certainly cause a change in its depth of cut.

I'd appreciate any wisdom anyone can contribute to this.

Best Regards

picclock

[DaveH]

Here’s my little bit of wisdom. (I always think age is a dear price to pay for a little wisdom). So you are getting it for nowt.

The fly cutter and it’s cutting tool should always be balanced and in it’s most rigid mode.

Making the sweep diameter bigger, (by moving the cutting tool) causes the fly cutter to become more unbalanced, and less rigid. 

I know the cutting tool seems to be adjustable, but the original intension was to allow the tool to be replaced or re-sharpened. Not stuck out to get a bigger sweep.

This is why fly cutters come in a range of sizes. (Cutting diameters)

That’s my little bit of wisdom not much I know, but sometimes every little bit helps.

Who remembers Sooty and Sweep then.

 
DaveH

[andyf]

Who remembers Sooty and Sweep then.
 
DaveH

 
Remember? As kids, my brother and I had the glove puppets. Endless arguments over who would wear Sooty and who would wear Sweep. Sweep was better, because he incorporated a squeaker. I suspect they are still in my brother's attic along with all MY  30 or so Dinky toy army vehicles. That Centurion tank cost me about 4 weeks' pocket money, and its Scammell transporter about the same.

Andy

[John Hill]

Actually John,

When cutting non ferrous, it is rather rare for me to take the flycutter off the machine, because I use it not only for very fine finishes, but mass metal removal as well.

John, my collection of tools for the mill is still rather limited, end mills, one face cutter (which I have yet to unwrap), drills and of course the fly cutter I made. My fly cutter take 5/16" HSS sticks of which I have ground a couple like your finishing style.