50 mm hole, how to approach ?

Plate is ordinary black steel, but is too long for the lathe faceplate, which

was my first thought. It drills reasonably well, but it is not free-machining.

The roundness or the hole or lack of it is not critical.

I do have a 1/3 Hp floor drill press and 1/2 hp 6x24 vertical mill,

but,

My largest drill bit is 1-1/4" Silver & Deming or 1" MT2.

I first considered drilling , then using a boring head

and taking off 0.10 mm per pass. (My boring head is MT2, which matches my mill and drill press. The drill press has has sloppiness in its runout.

Is there a better method to approach this task?

ps, it's for a friend and the steel belongs to him, so I don't want to botch it.

Thanks in advance,

Paul

Paul,

I would probably use either a Trepanning tool or a HoleSaw.

... With either tool, you can work from both sides of the plate.

MichaelG.

Edited By Michael Gilligan on 01/02/2014 17:34:48

I agree with you Paul and chain drill out the majority of waste, then file off the lumpy bits left and then finish off with the boring head

If you do the majority of the filing to the edge of the chain drilled holes the boring head should be able to cope.

I'd fix it to the mill table and work my way upto the largest drill and then switch to the boring head.

If you need a really good finish and don't have power feed on te mill then think about bolting it to the lateh cross slide and using either the boring head or a between centres bar and the lathes power feed.

J

Drill as big as you can and then use the boring head, trepanning and hole saws are a right PITA.

Tony

I have had good results using a trepanning tool on up to 6mm in a drill press but they are finicky. I would not want to try it in 32mm. But you have a mill and a boring head so it should be possible to grind a trepanning type cutter and take advantage of the mills stiffness and down feed / up feed to take light passes. In a drill press the tendency is for the tool to jam as it is very hard to regulate feed rate. Advantage of trepanning is you only remove a small amount of metal and the resulting slug can be used for something else.

Depending upon the swing of your lathe, drill large hole in the right position on the plate. Position the plate on an angle plate fixed to the lathe saddle using the drilled hole and the drill held in the lathe chuck. Clamp up. Use boring bar or similar held in 4 jaw chuck and feed the plate onto the tool. Adjust tool for perfect hole. EZPZ!

Ah! You have provoked another thought or two. You have convinced me to avoid the drill press.

I forgot that I have a rotary table.

Might I proceed as follows on the mill?

Place a thin hard board under the plate to prevent milling the rotary table's top face. Attach the sandwich of plate and board to the rotary table (there is room for four clamps). Maybe use double faced tape.

Then use a 6 mm center cutting end mill to slowly cut a 50 mm OD channel, stopping before the cut has reached the bottom depth of the plate, to avoid a jam-up from a loose 38 mm "wheel". Remove all and punch out the 38 mm wheel from behind. Clean up with a roundish file, or use a boring head (a precision not needed in this particular case).

Certainly, a lot fewer chips. A round piece saved for future projects. Maybe less work than chain drilling and filing? No risk of a "catch" of the boring head in the hole, given that a MT2 shank is a weak point, especially on an interrupted cut.

Thank you all for your collected and stimulating thoughts !

Paul

Edited By Paul Fallert on 01/02/2014 20:05:04

Edited By WALLACE on 01/02/2014 20:13:39

.

... and his friend ought to pay for that anyway

Hi Paul,

Do you know anyone with a 50mm Rotabroach type cutter they work like a trapaning type cutter and leave a slug of metal in the centre they have a spring loaded centre and an a ejector spring that when finished removes the inner slug like the ones you see with a hole saw,the finish is quite good and keeps to size with ease.

Regards

John

And with the arbor and delivery you see a total of £17.58!!

a bit off topic but my lounge stove fell to pieces before xmas as the cast iron flange on top to which the flue pipe and then flexible stainless chimney liner was attached to disentegrated!

the lugs that bolted the flange to the top of the stove had completely disappeared after 12 years - must have been some very poor quality cast iron.

anyway to effect a repair ive got to make a 6" dia hole in a piece of 1/4" thick steel plate - too big for my lathe or mill - though just possible on the mill by trepanning. chain drill and filing or making up a trepanning tool in the mill?

cheers,

julian

Julian, Sounds like an excuse to buy a small plasma cutter - or find a friend who already has!

Regarding 32 mm plate, hole saw is the way I went for 25 mm MS (4 x 6 mm plates in a sandwich).

Mark

Yes, you could turn up the arbor while you are waiting for the hole saw to be delivered.

In the meantime, Paul with his method and me with mine have both finished and supplied a happy customer.

Although I would consider that cutting that depth on a rotary table on a radius would likely result in a possibility of broken cutters if not careful.

And drills are cheap.

I have read a lot of assumptions about the thickness of this plate but the O.P. has not stated how thick it is. If it is 32mm then an ordinary 6mm slot drill will not reach more than just over half way as they are on average about 20mm long. I would suspect that a long series would also struggle and if the O.P. is not experienced then it will be expensive in broken slot drills. I would go for something like an 8/10mm slot drill far more forgiving.I favour jasonB's solution drill as big as you can and bore it.Having read the header I see the plate thickness is stated, I am a stupid boy! but my remarks still hold good.

Edited By Dusty on 02/02/2014 09:57:00

I wish to thank each of you for your thought provoking remarks.

You have certainly surfaced a number of different approaches.

I now recall (when making a follower rest for the lathe from 19 mm thick CRS) that I resorted to the use of metal cutting blades in a handheld (wood butcher-type) variable-speed jigsaw. It was slow going and I broke a blade, but it made a nice enough cut and required only a bit of hand filing to finish. Given that the 8mm (not 6mm) slot drill might not comfortably cut the total depth, the final cutout (after removing from the mill and drilling a starter hole in the slot through the piece), would be easy work for the jigsaw. Then the file would be used to clean up the rough edges.

Paul