Setting miller table true

I have to make 6ft lengths of Ali extrusion from solid flat bar. My mill has a 3ft table and 2ft stroke. My plan is to produce a jig about 8ft long with a series of clamps along it and fix it to the miller table.
This would support the bar and help stop it distorting during machining
I would take one cut and then wind back, move the bar back to the cutter, clamp and mill again.
Before we go any further, the alternatives have been well covered by my customer, the extrusion is discontinued, a new die will be 12weeks, minimum order is vast. We need only 15 legths and have 5 weeks to deliver the finished fabrication.
The problem is how to true the jig to the miller. I know how to clock it up by setting a DTI on the column and wind the table back and forth but my machine has a universal table that can be swung about 30 degrees left and right, I don't think this a problem in this application, just set the scale to zero and true as above.
Am I right in thinking this, if not how do I set the table true?
Also, in 50 years at this game I have never needed the table to be anything other but 'normal' so what is this feature for?
Remember, there is no fool like an old fool, thanks for your time in reading this and all help is appreciated as always.
Peter

I presume the machine has a horizontal spindle? Universal's are used for spiral milling where the table angle sets the helix angle on the part.

Setting the table true on such a machine is the equivalent of tramming the head of a vertical mill , it is to ensure the cutter is perpendicular to the work piece movement.

On my little horizontal, i usually just use two 123 blocks between table and column as a quick setting . You could set an indicator on an arm in the spindle and clock the table either side

#2 for Bills suggestion of clocking the table slots. Knowing the slots are true will make it much easier to set up the jig.

Can be a proper PIA to get this sort of thing set up well enough to avoid an objectionable mark or, worse step, at the junction between moves. Hopefully you have discussed with the customer what is acceptable here. No visible mark after machining is difficult to achieve. If it needs to be cosmetically clean expect to do a bit of polishing out.

Do take your time to make a good job of the jig and ensure that it doesn't try to droop. Use outboard roller supports if need be. With 15 to do investing time at the start so the job goes just like that is pretty much essential. It surprising how much a long piece like that will try to move under cutting loads given the chance. You will almost certainly need to clamp the whole thing not just the bit you are working on. I guess there must be some sort of resonance effects going on.

Last year I had to modify two 14 ft long sections on my Bridgeport and had a truly miserable time. With only two to do, and little more than an hours machining on each, I cheaped out on the jigging side with a simple fence and improvised supports. Very bad idea as I virtually had to reset each section individually after moving. Fence just got it somewhere close. Couple of days to do the job! A for me job so at least the customer couldn't complain. Much!

Clive

Put a couple table stops(Bar that fits in your table slots)one each end table make sure you have no burrs in your slots and dont push them down to bottom of slots-Clock the 2 posistions in.Might be better to move your jig leaving your job held in place to eliminate blend marks.Dont really know what your doing but if your doing something that has to be in line drill ream some dowell hole thro your jig to suit the size of your table slots(eg:-table slots 16m/m-Drill ream 4holes one each end other 2 equally spaced.Couple long dowells thro holes into slots for trueing jig up-Machine 2ft-leave job in jig loose clamps push jig along- and repeat if you dont release the job before completion you should be ok-Beware of swarfe under jig when moving

To put it all in a sentence you need to swing trammel the table centre tee slot from the machine spindle. The further the swing trammel the better.

Regards Tyrone.

I have succesfully produced long aluminium parts by pushing it throug a opening the size of the raw material then a cutter and then through a opening with the final size
Both openings clamped on the table In between some space and airblast for swarf clearance
Much -much faster
Depending on how you do it and which profile the beginning and end may be off size


Peter

Thanks for the input. I probably haven't made myself clear, I understand how to true the table to the column and the jig to the column as well, but what I can't decide is that if the table is say, 1 degree out and I set the tee slot from the column it will appear to be running true will my jig will also run true despite the table being out of line?
I too have tried pushing material through a jig to make a section, in this case the metal removal is too great.
Peter
Peter

it will cut as straight as as table ways whatever the angle but the cutter will be at an angle so won't necessarily cut the shape it is supposed to (although this can be useful if you want a curve or want to force the work piece to one side to keep it against a fence)

bill