View Full Version : how did they machine it.

dr pepper
10-21-2009, 02:46 AM
Took mi pillar drill apart, an old brit fobco, and noticed that the shaft the driven pulley fits on above the quill has a hole through it with a key, no problem, but on closer inspection what I thought was a hole with a key slot and a key isnt, its all one piece, fobco have machined a hole with a integral key protrusion.
I've tried to remove what I thought was the key and its deffo one piece.
How did they machine that one out then.

10-21-2009, 03:20 AM
Well, hmmm.

It's a degenerate splined hole, of course...
At home, one could furnace braze the key in place.
One could imagine a special broach to do such a thing.
If this were some sort of alloy rather than cast iron, it could be die-cast.

- Bart

10-21-2009, 03:43 AM
They probably broached it.

dr pepper
10-21-2009, 06:11 AM
I wondered about a broach, I have little experience of broaching, 'cept for using a rotor broach for bashing big holes in concrete flooring to put machine mounts in.

Doc Nickel
10-21-2009, 07:00 AM
It could have been made on a shaper or a slotter, too. Several of my books show rotary-table like devices for standard shapers for doing splined holes, and of course most slotters have such a table built in. Might be more likely than a big broach.


dr pepper
10-21-2009, 07:59 AM
So if you were using a slotter then, you'd drill a smaller hole, and using the slotters cutter and the rotary head slot out the hole bigger, but skip the bit where you'd want the key to be, that makes sense, fobco probably had a slotter with auto feed and adjustable limit switches for semi auto operation.
When I've been stuck here at work, I have done splines on the lathe, heath robbo but I put felt tip marks on the drive gears to indicate postion with the lathe in a low gear so that the motor did lots of turns per turn of the spindle to improve accuracy, and whilst holding the foot spindle brake used the apron handwheel to drive the cutter through (previously surface ground to the size of the key), sort of a crude shaper, I've done this a few times since to do keyways on pulleys.

10-21-2009, 10:17 AM
Sintered metal,I've seen plenty of sintered steel spockets with intregal keys.

dr pepper
10-22-2009, 07:00 AM
I must be a bit fick, whats the issue with sintered, is it cast in the exact shape?.

10-22-2009, 08:05 AM
It's powder metallurgy. Metal powder is compressed under extreme pressure and high temperatures in a mold so it forms a solid mass of metal at net required shape. Depending on the process it can produce a close equivalent to cast iron or even hardened steel. It is a very common process.

Here is an example of keying two gears together. Powder metallurgy can be so accurate as in this example that it is a perfect finger light press fit. These gears are equivalent to hardened 4140 steel.


10-22-2009, 08:55 AM
Sintered metal is recent technology and the drill press probably predates it by several decades. If the gear is a casting, the bore would possibly have been rough cast and broached. If it were a steel gear, it would also be broached.

Use of a shaper would work, but be too slow for a manufacturing environment. Broaching would be the method of choice. Industrial broaching machines and broaches are quite different than the keyway broaches used in home shops. The broaches can be several feet in length and are used to produce a wide variety of shapes in a single pass.

10-22-2009, 11:44 AM
Use of a shaper would work, but be too slow for a manufacturing environment. Broaching would be the method of choice. Industrial broaching machines and broaches are quite different than the keyway broaches used in home shops. The broaches can be several feet in length and are used to produce a wide variety of shapes in a single pass.

Is it true that "some" automotive engine blocks are "planed" flat with a broad flat broach supported from the back?

10-22-2009, 12:55 PM
I don't know for sure, but have little reason to doubt that the procedure could be used.

Broaching and broaches represent a whole other machining process not often encountered in the home shop. It is widely used, perhaps less now than formerly due to CNC and EDM advances, but it is a relatively inexpensive and low tech means to produce forms not readily achieved by other means.

It is widely used in the firearms industry to produce cuts not possible by other means, the chase for the bolt in a bolt action receiver or a magazine well for instance.

10-22-2009, 01:05 PM
Looks like I shoulda searched this B4 askin'

This is interesting reading for anyone even mildly intersted in broaching. Not home shop operations, but still interesting...http://books.google.ca/books?id=6PE0jZZ-nr0C&pg=RA1-PA385&lpg=RA1-PA385&dq=engine+block+broaching&source=bl&ots=vd64VYn0Hr&sig=QZTEjHcjMw7x2mTeyEWdDinFJzw&hl=en&ei=J4LgSr6CG4zOsQORytT2CA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBIQ6AEwATgK#v=onepage&q=engine%20block%20broaching&f=false

dr pepper
10-23-2009, 03:48 AM
Well thats interesting, I thought I was well versed in manufacturing, I've worked all over maintaining all kinds of machines from junk to aerospace high tek.
We had those machines at leyland motors, I remember seeing the broaches in racks, only at the time and untill now I didnt know what they were (showing my ignorance).
I do have experience of grinding machines as per the article though, they were one of the most unreliable machines, and being maintenance we were the first to find that out.
I'm guessing that my example is broached as the unit is made from steel and the outer edge has witness marks from machining.
Thanks for the explanation chaps.

10-23-2009, 06:53 AM
Broaches were used quite extensively for volume engine block machining. I remember a two or maybe three high broaching machine (could do three blocks in one pass) that finished the sump face and I think one side of the block in one go. This was a massive machine, larger than the one in the book illustration. Every time it made a pass the very substantial concrete foundations would shake. I was working in a reference room (inspection) not far away and that had its own foundations with rubber dampers to try and isolate it from the vibration of that machine and others. It was not wholly successful.

The broaches used in these machines were very complex and needed to be reground by very skilled people. Considering that they were cutting cast-iron without much more than initial fettling, the broaches had a hard life, but they were capable of working to close tolerances.

Dr Pepper - the mention of Leyland Motors makes me think that you must be fairly close by. I am north of Preston.

10-23-2009, 12:59 PM
A little bit about powdered metal technology.

To begin with, sintered products (as we know them) have been around for several decades. One of the earliest products made from powdered and sintered metal, was the Oilite bearings. If my memory serves me correctly, Oilite bearings were developed in the late 30's, and I think Chrysler was the leader in this field.

If you use carbide tooling, you are employing a powdered metal product.

The process is rather simple. Grind your base metal to the required granularity, add a ground filler or matrix metal to bind it, and press hell out of it to hold the mixture together. After molding the part, you simply heat it in an oven (sinter) till the matrix diffuses throughout the base metal structure. In its simplest terms, you are "sweating" the base metal molecules together.

There are other processes in use now that employ different methods, mostly to obtain greater accuracy of the part, increased strength or other structural qualities, or shorten production time. The basic formula is still pretty much the same though.

10-23-2009, 03:14 PM
It's powder metallurgy. Metal powder is compressed under extreme pressure and high temperatures in a mold so it forms a solid mass of metal at net required shape.

Isn't it more common to press the powder in the mould, extract it from the mould, then sinter it?

10-23-2009, 04:08 PM
No, the process is called Hot Isostatic Pressing (HIP)


It doesn't use a press but instead compressed inert gas to densify the material at pressures up to 15,000 psi.

The process to produce these near net shape parts is fairly straightforward. The end user supplies Crucible with a drawing of the finish part with nominal dimensions and machining tolerances. To determine the HIP shape, overstock is added onto finish dimensions to yield a near net shape. The container design is established and drawings are generated in order to fabricate cans, which are usually made from steel tubing, pipe, and/or formed sheet metal. Can components are welded together and fill stems are added for loading of powder into the container. After welding, the container is leaked checked to ensure the can is hermetically sealed. Powder is loaded into the container, and the part is consolidated and brought to full densification by HIP. Because of the void space between particles in the as-loaded container, the compact shrinks during HIP to a smaller size than its original pre-HIP shape. Anisotropic shrinkage often occurs due to the part geometry, heating and pressurization rates prior to the HIP hold cycle, material properties of the powder, and container material, thickness, and position of the welds. Design methodology is critical to ensure dimensional control.

10-23-2009, 06:29 PM
Powdered Metallurgy is a fascinating, relatively recent development.

A direct quote from the site below... "In reality, PM comprises several different technologies for fabricating semi-dense and fully dense components."

I'm guessing semi dense components would be like the oil lite bushings where the permeable void space, once filled with oil makes the bushing self lubricating. Fully dense components might be gears, etc.

According to this site, there are four sub sets of processes. "Press and sinter", MIM or "metal injection molding", HIP "hot isostatic pressing", and "powder forging"


Which powdered metal process applied would be dictated by application, economics, access to equipment and the almighty $ as in cost per unit of both capital investment and input materials.

I've only ever personnally seen the cold process, but a flow chart of alternates is here http://www.mpif.org/IntroPM/process.asp?linkid=2

FWIW, the cold process was for shaped charge liners.... Now that was a field trip ;)

Your Old Dog
10-23-2009, 09:12 PM
............. Powder metallurgy can be so accurate as in this example that it is a perfect finger light press fit. ..............

Correcto-mondo Evan! Triggers and hammers are made from cintered metal process for Smiths and Colts and most others I expect. That the sear is so critical is testament to how accurate they are.

10-24-2009, 12:23 AM
One process I used for making shaped holes in machined parts was hot broaching. An oversize punch is made in the shape of the hole. There is no taper on the body of the hot broach and there is a tapered tip on the punch that expands the part. A part blank is drilled with a smaller hole and then is heated red hot. The punch is then driven through the hole to put in the shape and removed before the part cools. The hot broaching process only takes a few seconds. When the part cools down it shrinks enough to come to the correct size. The part is then put on a shaped mandrel and turned.

This was a common manufacturing process in the late 1800's and early 1900's when making broaches were relatively much more expensive. I last used it in 1989 to make collets for a hand tool designed in 1902.

dr pepper
10-26-2009, 11:52 AM
Fascinating chaps.

Hi willmac, yes I'm not far off, I work in garstang and live in preston too, up by the tickled trout.
If you've seen a worn out camo land rover or a fiat punto with overgrown aerials thats me.

If you ever visited the fab shop at leyland then you will remember the watkins and mitchell 1200 ton power presses, they made the floor shake too, we took one out, the cushion cylinders went into the floor a good 8 feet.