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plunger
08-22-2011, 01:05 AM
I have an iso 40 milling machine. I need to make some jigs that require 5 holes of 47 mm and they need to be 15mm deep. How does one go about removing such large holes My biggest drill is 25mm. I also have a standard 50mm boring head. Do I rather use a end mill and rotary head, Its important that the bottom is also smooth. The plate is to big to mount in a lathe.
Thanks eugene

darryl
08-22-2011, 01:52 AM
I built myself a custom boring tool just for doing that. It is adjustable on the fly, so you set the maximum diameter for it to go, then wind it in to the minimum to start. You set a depth of cut, then when it's running you hold a finger in the right spot and as a tab comes around, your finger knocks it and the tool advances. You basically take out layer after layer until the depth is reached, then you can set it and clean up the diameter by lowering the spindle in the regular fashion.

The normal way would be to set a depth stop for the spindle for the depth of hole needed, then bit by bit enlarge the hole until you reach the diameter you want. You have to start and stop for every adjustment of the boring cutter. Tedious, but it works. If you're boring a hole that's deep relative to the diameter, this is probably what you'd do. If it's shallow relative to the diameter, it becomes very time consuming, and something like what I made would be a better solution.

In any event, all the material that's in the way of the final hole has to be removed. I don't know of a way to remove most of it in one chunk-

winchman
08-22-2011, 02:02 AM
"You set a depth of cut, then when it's running you hold a finger in the right spot and as a tab comes around, your finger knocks it and the tool advances."

Please post some pictures of that tool.

darryl
08-22-2011, 02:36 AM
Found a few pics in my archive of photos. Here they are- the first pic shows the upper side of the tool, which is recessed to fit the mill spindle. The central threads are for the drawbar. I can either use a longer drawbar for this, or I mount the extension piece I made so I can mount all my different accessories using one drawbar. To the left is the adjustable stop to control the maximum extension of the cutter, and to the right is the operating wheel. I called it a tab in my first post, but it's actually this wheel that you touch with your finger.

http://img.photobucket.com/albums/v136/heinrich/boringhead2.jpg

Second pic shows the bottom, or business side of the tool. To the left is the gearbox that turns the leadscrew to adjust the position of the cutter. The cutter is shown mounted, and you can see some tapped holes which allow you to move the cutter relative to the base that it's mounted on. You can get it to swing over 3 inches, in other words you can mill a recess over 3 inches in diameter. You can also get it to start from a center hole in the workpiece that's only 1/4 inch diameter. You can easily see the leadscrew that moves the cutter mounting base. The base and the two flanking guides are dovetailed.

http://img.photobucket.com/albums/v136/heinrich/boringhead3.jpg

A better view of the cutter. You can see the leadscrew that moves the mounting base for the cutter, and to the right is the adjustable stop.

The leadscrew drive gears are actually from a guitar string tuner. I do plan to replace the toothed wheel with something more suitable one day. It is a bit hard on your finger when the teeth have to skid to a stop on your skin in order to advance the wheel.

The cutter can be turned around and with the spindle running in reverse, the adjustable-on-the-fly system moves the cutter inwards rather than outwards.

http://img.photobucket.com/albums/v136/heinrich/boringhead1.jpg

lakeside53
08-22-2011, 02:36 AM
I have something similar for my BP - a Lagun "automatic boring/ facing head". Works well... but I don't use it much now I have cnc control.

Several types on ebay.

Peter.
08-22-2011, 05:22 AM
Hey Darryl if you changed that toothed wheel for a spoked wheel and turned a knurled ring to run on the OD of the body with a peg on it you could just stop the ring with your finger and the peg would advance the wheel once per revolution.

That's a very cool tool though!

Ian B
08-22-2011, 07:58 AM
Eugene,

First question - how many of these holes do you have to make in total? If it's a lot, then it might be worth buying a used 47mm drill, and grinding the tip flat. Drills are a very quick way of making holes, working with boring heads goes much slower as you have one unsupported cutting tip instead of two balancing each other.

You may be able to use a U drill, which is basically a spade bit with replaceable carbide inserts of the diameter you need - these may be made with flat tips rather than the usual drill point.

You have a boring head, to do this (and produce a flat bottom) you need what Darryl shows - a boring and facing head. Wohlhaupter & Narex make lovely ones, either look on Ebay or take out a second mortgage for a new one. Even with these, though, boring to close tolerances is time consuming.

Is there an easy way of repeatedly mounting the workpiece on a rotary table and using (say) a 25mm diameter end cutting end mill? Plunge to depth, rotate the R/T through 360 degrees. Keep the x and y slides locked in position, and once set, it'll repeatedly produce the same size of holes. Pilot drill the 5 locations, then indicate on a pin dropped in the pilot hole to properly locate the workpiece on the R/T

Ian

David Powell
08-22-2011, 08:10 AM
I have found that even cheap holesaws can be useful in roughing out for large holes, They tend to cut well oversize so consideration should be given to an adequate margin for error. Grinding out every other tooth helps with chip clearance. For a 47 mm hole I might well consider using a 1 1/2" holesaw then boring it. It all depends on the machine, the tooling available and the operators skill. There is probably no right answer, just some which fit the circumstances better than others. Regards David Powell.

David Powell
08-22-2011, 08:13 AM
Sorry to waste your time, only useful for through holes ! David Powell

MrSleepy
08-22-2011, 09:14 AM
My FILs neighbor sold me a Wohlhaupter head thats in really good condition withs its box and accessories for 50...

When I went round to collect it.. He'd sat a Unione (D'Andrea) TS1 boring head on top...and said "you can have that if you want it"..

In some ways I prefer it over the Wohlhaupter as you can increase the diameter of cut without having to stop the head.

If I had to do a few I'd drill it out and finish it of with the TS1.. If I had a lot to do I'd look a getting a Rotobroach annular cutter to cut the outside...then drill the middle and finish the middle of with the TS1..All depends on how accurate it needs to be.

Rob



http://i897.photobucket.com/albums/ac180/MrSleepy123/BoringHeads.jpg

Peter.
08-22-2011, 09:26 AM
How does that work? Do you hold the center from turning and use the crank to advance the dovetail?

MrSleepy
08-22-2011, 09:40 AM
How does that work? Do you hold the center from turning and use the crank to advance the dovetail?

Exactly...The bar on the top stops the top section with the crank handle from spinning...cranking the handle one revolution advances the cut by 0.050 thou.. It also has a 2 speed autofeed with stops if needed.

Rob

Toolguy
08-22-2011, 10:07 AM
A low tech way to do it would be to use a hole saw as mentioned above and cut a little short of the depth. Everything inside the holesaw cut can then be cleared out using a regular endmill and X and Y handles, being careful not to go outside the circle. Then the hole can be bored out with a regular boring head to bring the hole out to the final diameter.

MrSleepy
08-22-2011, 10:17 AM
A low tech way to do it would be to use a hole saw as mentioned above and cut a little short of the depth. Everything inside the holesaw cut can then be cleared out using a regular endmill and X and Y handles, being careful not to go outside the circle. Then the hole can be bored out with a regular boring head to bring the hole out to the final diameter.

If you cut the outside first with a rotobroach annular cutter..then x-y mill the interior..you'd only have to find the centre point for the first operation..which could save a lot of time if you have many holes to do.

macona
08-22-2011, 11:18 AM
Cut out square holes and then make inserts on the lathe with the correct bore to drop back in.

strokersix
08-22-2011, 12:02 PM
A low tech way to do it would be to use a hole saw as mentioned above and cut a little short of the depth. Everything inside the holesaw cut can then be cleared out using a regular endmill and X and Y handles, being careful not to go outside the circle. Then the hole can be bored out with a regular boring head to bring the hole out to the final diameter.

This is what I do minus the hole saw.

Layout a circle, then clear out with an end mill X,Y close to the line, then bore to size. I've suggested this before and received objection to interrupted cut with the boring head. Not sure I understand the objection. I suppose if you are running a small mill/drill then the interrupted cut might be an issue but then a hole saw would be too with a light weight machine.

Arthur.Marks
08-22-2011, 12:42 PM
Plenty of good ways suggested already. The 'poor mans' facing/boring head is a rotary table and end mill. If you use one small enough, it won't chatter at the bottom of the cut. Then you rotate around with increasing diameter on the rotary table until you are to size (47mm diameter) and leave a small amount for a fine finishing pass on the bottom (15mm depth). Probably lots of set-up to accommodate fixturing to the RT, however.

Carld
08-22-2011, 03:22 PM
If the holes are 47mm diameter x 15mm deep then they are pockets. I would use and endmill to form a pocket 3/4" diameter by 15mm deep and then use a boring head with it set to depth to finish out the pocket to the 47mm diameter. You will have to take .050" cuts on each pass to finish size. You may be able to take .100" each pass but you have to try it to see.

mike os
08-22-2011, 03:33 PM
from the title I was expecting to see john attacking his favourite machine with a big hammer :D

Don Young
08-22-2011, 09:24 PM
I don't know if a useful way to do it could be devised but I have read that a twist drill is the most efficient of the common metal removal tools. Maybe 'Swiss cheese' most of the metal out and then switch to a boring tool or a large end mill.

jkilroy
08-22-2011, 11:51 PM
47mm is 1.850 inches. I'd get a 1.75 end mill...

http://www.ebay.com/itm/Roughing-End-Mill-1-3-4-x-1-1-4-x-4-x-6-3-4-3FL-R-312-/190554116152?pt=LH_DefaultDomain_0&hash=item2c5de91038#ht_1655wt_1110

And cut those pockets to depth with a big cutter like that, and then bore out the rest. Evan a 1.5" cut will save you LOTS of time.