centering ect on mill

[timeone]

I knew one day id have to ask this question as today i tried to mill a bracket i need for my bike but after doing 2 and messing up i need help
basically im making a ring 50mm id 55 od and cant get the same thickness all the way around so im not centred correctly
Before you ask i dont own any kit to centre things only a dial gauge
so in simple terms the easiest way to do it.

Jason

[DaveH]

Jason,

errrrr........... you do have a rotary table?

DaveH

[timeone]

yes indeed i do

[DaveH]

Jason,

Sorry mate, which are you cutting the 55 or the 50

DaveH

[Jonny]

Quite a bit of trial and error then, had to re centre my chuck again on RT this afternoon for doing exactly the same.

Will have to keep rotating RT and adjusting the runout of said part until adequate. Dial guage will be ok.

Alternatively dont bother if using a larger piece and can bolt down to RT. I/D will be same as O/D but would have to leave two lugs where clamped, unless you feel brave

Is this just a 55o/d x 50i/d collar or tube?
Best done on a lathe.

[timeone]

Its not a circle eg tube im doing so lathe is not possible

im cutting both id and od   the id is a complete circle where as the outer will have a lug sticling out ill saw cut through this as it will the bit i put a bolt through to clamp it

abit like this but one piece
http://www.allproducts.com/metal/daizan/02-l.jpg

[BillTodd]

Centre the rotary table and spindle first: If you don't need any super precision you can just do it with a cone shaped something in the chuck, else fix the DTI to the rotary table (ro-tab) and indicate the round part of a end mill in the chuck while rotating the ro-tab. Zero your dials. (see: http://madmodder.net/index.php?topic=3776.msg41242#msg41242)

Without moving the X,Y or the head, centre the work-piece on the table using a pointy thing (parallel lathe centre)  in the chuck, or a DTI mounted on a bar hanging off of the chuck rotating by hand around a reference on the work-piece.

I would fix the work-piece so you can do most of the work on the outside of the piece first  - you will probably have to clamp around the outside  so will have to move at least one clamp during the process (always keep the piece clamped by at least two clamps, while you move one of the other clamps - will will soon find out your ro-tab is not big enough - they never are)

Before you start cutting the inside, recheck that the piece is centred by moving your X & Y back to zero, with the afore mentioned pointy thing in the chuck. Then rotating the ro-tab to check it remains under the point.

Cut or bore the inside as required.


Bill

[DaveH]

Jason,

Ok I understand. First align the centre of rotation of your RT to the Zaxis (do you know how to do that)? Using X and Y axis.

After the RT is aligned you will then need to lign up the centre of the 50 and 55 circles to the Z axis (which is allready aligned to your RT). Don't touch the X and Y handles.

Move your work piece untill the centre is aligned with the Z axis then clamp the work piece in place.

You may to check whilst clamping.

Have you followed this.  Come back and ask Jason if it is not very clear.


 
DaveH

[timeone]

Thanks Guys
I think ive got that ok
Not to bad off space wise as my rotary table is 8inch so the part only takes a small part of it but ill do as you say and make sure its bolted down well.
I need to pay more attention to centering things up as i now realise there is a lot of it in milling work
the mill ive got is an oldy but still pretty good and works well. and will do most things i need it for. im not that jenned up on milling infact im only just getting the hang of a lathe again, after more than 35 years still its good fun

[andyf]

What a nice looking mill!
I see it has a barcode on the base. Was it a cheapo from Aldi or a posh one from Waitrose? 

Andy

[BiggerHammer]

Definitely a nice looking mill. Must have been a PITA to drag that thing across the barcode scanner in the checkout line. 

[timeone]

Funny the barcode sticker

That was the transport company
I bought this machine from Scotland and had it sent down to me in Dorset on a pallet by palletline cost £50  cheap as chips as they say.
was a bit of a problem getting it up my drive way but the driver was very good and got the job done. gave him a drink for his extra effort.
The fun started when i had to get it of the pallet i hired an engine lift but the pallet was to big and the legs of the engine hoist wouldnt go around enough to get the hook in the centre so i blocked up under the pallet and cut the corners off. after a few attempts the engine hoist was in position. and lifted it fine, me and the wife then manhandled to thing into postion
My lathe though quite small was split in 2 halfs when i bought it and i got it in the estate car and drove it the 100miles home. a helful fried was able to help lift it out and reassemble
 

[picclock]

Hi
Since no one has mentioned it, possibly the best way is to cut the inside and outside cuts on the ro-tab at one time. You need to ensure the ro-tab and spindle are aligned accurately as above. Lock the X axis if you can. If you have a Y axis dro then zero it here. Then clamp the corners of the square piece of metal you are making the part from centrally on the table - just by eye - with a piece of 3mm mdf or similar underneath. Then using a small mill, say 3mm cut the inner circle, setting the Y table position to the radius - 1/2 the cutter width.  Clamp the work from the inside to hold it for the final cut, if this is not possible leave two or three places to hold the work when its nearly cut through. Proceed to cut the larger diameter, again by adjusting the Y axis but this time to the outside dimension. Remove the part and cut through the thin holding pieces if you needed then and finish as required.

With this method the part will be perfectly concentric to within the limits of your equipment.

Best Regards

picclock

[timeone]

Well i managed to make my bracket though not perfect it is a good attempt
i found some of the cut was kind of rough i tried several cutters but got the same effect so maybe someone could suggest what went wrong

I ended up making it in 10mm then cutting to about 8mm then turning over once done and milled until it dropped out
Took about 3 hours to do but next time ill be quicker and better
ive got to trim the ends to size and saw cut down the middle of the smallest end so nearly done

[picclock]

To get best finish cut to within 1mm or so then use a really big cutter - 20+ mm and progressively remove the rest, making the last cut around 5 thou. Assuming Aluminium, lube with paraffin or WD40 at least on the last two cuts. Cut from one side only into a piece of MDF or similar to prevent damage to the rotary table, with a full depth cut.  Use brush to remove swarf between cuts. Ensure column is locked for best results. Could climb mill for the last cut if your really picky 

I've done bigger than this (5" inside - 6" outer) in steel and aluminium and apart from it taking time it seems fairly straightforward. I hacked out the centre(s) with some 3mm carbide endmills at flat out speed (for my mill). Broke a few due to too much feed and slot not cleaned out  . Trick for finish seems to be really fine well lubed last cut with V large endmill.

Hope this helps

Best Regards

picclock