Fly Cutting Woes

[ScrapMaker]

Hi all,
first post here, been lurking for a while but now I need some help!
Bought a used mill not so long ago, just got round to setting it all up.
First of all I put a dial indicator into the chuck, fixed the quill and put a setup block underneath it, zeroed the indicator.
I started at the left side, then done the same for the right side, over the 14" of travel, it moved by one thou, pretty good I thought.
Next came the vice, made sure it run parallel to the spindle, then run over a dial test indicator along the fixed jaw, and jaw base.
All of these measurements came in to under a thou. All was well, or so I thought.
Installed a fly cutter, one pre mounted into a morse taper. Setup a piece of Ali into the vice on a pair of parallel bars,
tapped it down and then tightened the vice a little more. Touched off the fly cutter on the surface and brought the quil down 10 thou.
All was going well with an excellent finish, working from right to left, then when the tool came in contact with the ali on the return stroke
after 3-4 inches of cutting so far) the tool started to cut again, and a step was machined.
Not being one to give up, I tried another fly cutter in a collect chuck, with the same result.

With everything being clocked to within a thou, is there any reason why I am getting a step between both sides of the cut?

Thanks

ScrapMaker

 

[Mike N]

You may need to tighten up the Gibbs. Is it a Bridgeport type mill? Did you rotate the spindle 360 degrees with your indicator to tram in the head? (left to right / front to back) On a 6" dia. swing you should be able to get it within a thou. Your flycutter won't drag on the backside if the head is straight & the table is tight.

 

[stevehuckss396]

You might try to tram the head again but use a collet instead of a chuck to hold the indicator. If the chuck has any wobble in it, it will affect the accuracy of the setup.

 

[kustomkb]

What kind of vise are you using?

Sorry to be a total newb, but are tools such as flycutters held in hobby mills by Morse Tapers?

Is there a draw bar as well?

thanks.

 

[ScrapMaker]

This is roughly the same mill that I have http://www.axminster.co.uk/product-Axminster-RF31-Vertical-Mill-Drill-21299.htm
It's a 4" milling vice, of very good quality.
The tooling is tightened up with a draw bar into the taper, then loosened and tapped out with a soft low hammer.

I think I may have found the error in my setup though.
The way I have checked it so far is just checking that the table runs parallel directly under the spindle.
Where the dial indicator is held in by the chuck it isn't checking that the spindle is perpendicular to the bed.
What I should have been doing is keeping the spindle in the centre of the bed, and indicating out from that to the extremes of the bed, that should tell me whether or not I am perpendicular.
I was in the middle of making up a little rig to do this anyway, I'll have to finish it first and then see what the results are.

Thanks for the help so far

 

[Jasonb]

You need to tram the head, the symptoms you have are caused by the spindle not being perfectly at 90degrees to the table. A search on hear should throw up a few methods of doing it.

A quick way to eliminate everything else is to do the same type of cut but from the oposite direction, the lower edge of the flycutter will cut first and the following edge should clear the work.

Jason

 

[deere_x475guy]

This is roughly the same mill that I have http://www.axminster.co.uk/product-Axminster-RF31-Vertical-Mill-Drill-21299.htm
It's a 4" milling vice, of very good quality.
The tooling is tightened up with a draw bar into the taper, then loosened and tapped out with a soft low hammer.

I think I may have found the error in my setup though.
The way I have checked it so far is just checking that the table runs parallel directly under the spindle.
Where the dial indicator is held in by the chuck it isn't checking that the spindle is perpendicular to the bed.
What I should have been doing is keeping the spindle in the centre of the bed, and indicating out from that to the extremes of the bed, that should tell me whether or not I am perpendicular.
I was in the middle of making up a little rig to do this anyway, I'll have to finish it first and then see what the results are.

Thanks for the help so far

ScrapMaker it sounds like you have found your problem and once you get the mill truely trammed I think you will be fine.

 

[ScrapMaker]

Well I've got it all measured out now, the average difference between one side and the other was 0.482mm, thats over a 380mm span.
The base is 150mm so I've calculated that it needs shimming by 0.1928mm, does this calculate correctly?

Thanks

 

[Jasonb]

I make it 0.19026 150/380 x 0.482

Bear in mind the shim won't be acting right at the edge of teh column base it will be itw width in so if the shim is 10mm wide then you should calculate over 140mm (150-10)

Jason