Machining Setup's with Few Comments

[neanderman]

The latter is the classic way to apply gold leaf. Don't know it it will work with your material.

[pete]

I've got a Slater Tools rotary broach I bought before the multiple shop made designs started turning up. Your right Carrdo $$$. Today I think I'd try a home built version before investing that much. There's at least one rotary broach kit I know of, http://www.hemingwaykits.com/acatalog/C ... roach.html However I've not read any forum posts anywhere about just how well designed there kit really is.But I don't know of any Hemingway Kits that aren't designed and tested to work well. Yes high carbon home heat treated broaches can be made and used if you've got the equipment to do so, as well as probably a surface grinder for final sizing and sharpening. Someone with a fair amount of experience could probably do the heat treating with just a torch. I'm not that confident I could do so well enough. Slater broaches are fairly expensive at $50 + + each depending on the profile and complexity. But at least then you know it's an engineered design that has the durability. Using there broaches in a home built rotary broaching head is probably the route I'd also go. Traditionally internal squares like that in both models and full size were just drilled and filed square when the numbers are low enough. It takes a bit of experience, A good sharp layout, a few needle files and a critical eye, but it's not too bad if you do a few test pieces first. Personally I think the rotary broaches excel at what they do on blind holes where almost nothing but maybe EDM could do the same. For those through square holes, a standard multi tooth square broach while still fairly expensive would last a few lifetimes with model work, and do the job in seconds.

[Carrdo]

TomMakeHere on Etsy (he is from Australia) sells rotary broach plans or will build an entire unit for you at a significantly lower cost than any of the commercial rotary broach manufacturer's (Polygon, Slater or Somma) but it is still a significant cost (the built unit). He does say that for home shop use his design is fine but is not intended for heavy duty commercial applications. He has good feedback but I have not bought or used anything he makes.

I have looked but have not found any commercial standard multi tooth square broach that is available under 1/8" square. I have found a website where it is shown how to make such a multi tooth square hole broach but there is quite a bit more to it than what is presented but yes, it can be done (made in any size).

[Carrdo]

Another job that has been waiting about 7 years for me to get around doing it.

At that time I was at a machine tool dealers buying some collets which he was selling relatively cheap for the Herbert 2D capstan lathe.

While there, I spotted what looked to be a new right angle attachment for the Millrite. The dealer said that it had a unusual (unknown) tool holding taper (not an R8) and as a result he would sell it to me at a very good price. The right angle attachment bore no makers name but it looked to be extremely well made with a fine substantial housing casting. The spindle quill locking taper however was an R8 so it would fit the Millrite here. I would hazard a guess that it was made in Taiwan.

I took a chance and bought it. The funny unknown tool holding taper turned out to be a #3 Morse taper and as I had lots of #3 Morse taper tooling I was very happy.

The housing casting bore was 3-3/8" exactly so it was meant to fit the quill of a Bridgeport or a Bridgeport clone. Unfortunately, the Millrite has a 3-1/4" diameter quill so to be able to utilize this unit a very thin sleeve would have to be machined. Millrite right angle attachments do exist but they are very rare and when one does come up for sale either new or used they are outrageously expensive.

The problem with having such a thin sleeve is the sleeve has to be machined exactly to the size of the Millrite quill and exactly to the bore of the right angle attachment. Not only does it have to be on size, it has to be truly straight (not tapered in any way) and truly round. This is not so easy to achieve when one has a finished wall thickness of only 1/16" or slightly less over a length of just under 4" long which is what length the sleeve needed to be.

Another decision which had to be made is what material to make the sleeve out of. I ruled out steel as I do not want to have a steel sleeve clamped to a steel quill but a somewhat softer metal. So one can pick either cast iron, brass, bronze or aluminum. What was readily available here in the size I needed quickly ruled out the first three materials so, in the end, I bought a 5" long piece of 6061 aluminum tube having a 3" ID and a 3.5" OD. I thought I could have used a somewhat thinner walled tube and saved some $$ and prevent having to machine most of the wall away but this proved to be the right choice as the OD of the tube turned out to be neither round or concentric to the ID of the tube with the OD and ID surfaces both having a lot of dipsy doodles. The last one inch of the blank was to hold the blank in the 4 jaw and with it not being turned down, the distorting effect of the holding jaws were minimized.

To digress a bit, when installing a right angle attachment to the quill of your machine, there are usually found two end clamping cap screws with a centre set screw spreader. To install the right angle attachment, the clamping end screws are first backed of and the spreader set screw is then snugged up and when snug just give it a further 1/8 of a turn and no more. DO NOT OVERTIGHTEN THE SPREADER SET SCREW or you risk breaking the housing casting. There only needs to be about a 0.002" gap on the quill diameter and with that gap the right angle attachment should slide over the quill if things have been aligned and then fully seated. I sometimes use a little light oil to help with this operation. Once on the quill, the spreader set screw can be backed off and the two clamping cap screws can then be tightened.

For the actual machining of the aluminum blank itself, the last three photos show all of the tools and pre machining preparation work which first has to be carried out.

to be continued.

[Carrdo]

Because of all of the dipsy doodles inherent in the blank, the blank was first centred in the 4 jaw chuck near the chuck jaws and then the indicator was run along the length of the blank to the outer free end where the blank was centrered here as true as possible. I did this several times to try and average out the error in the blank. Needless to say the blank did not run true at any setting but with such a thick wall, I could turn both the ID and OD straight and concentric if everything was done at one setting. Use a very stout boring bar, a sharp tool bit preferably honed after grinding, light cuts and the finest automatic longitudinal feed the lathe has as one is also trying to achieve the best possible surface finish possible.

Your measuring equipment has to be up to this task also. I used two of my best vernier calipers and an inside micrometer to measure the bore ID as it progressed. Both vernier calipers had to read within 0.001" of each other and to the final measurement made with the inside micrometer. A lot of this is "feel" and practice, practice. The final bore was made 0.002" oversize to the diameter of the Millrite quill as measured with my best micrometer.

Then, all at the same setting the end of the blank was accurately faced and a chamfer turned on the free end of the blank which was the same taper angle as the pipe centre. Fortunately, there was still enough wall thickness on the blank at this point to prevent it rigging like a bell but soon there wouldn't be.

Then it was on to the turning of the OD of the blank as seen in the second photo. Again the OD of the blank was turned to 0.002" undersize to the bore of the right angle attachment.

Care, patience and nerves at this point as the spacer wall is now so thin, it will chatter and ring like a bell without the pipe centre fully supporting the free end of the blank at all times. Hence the lathe centres have to be in perfect alignment. Sharp tool bits, fine automatic feeds and depth of cut are a must also to achieve the best possible surface finish.

to be continued.

[Carrdo]

The chucking end of the sleeve had now to be cut off.

I did not dare to do this in the lathe so I took the piece to the bench vise and gently clamped it between its soft jaws and proceeded to hack saw (with a 32 tpi saw blade) the chucking piece end away while holding the work steady in one hand and carefully sawing through with the other.

The now separated sleeve section was then returned to my smaller lathe and clamped internally with the outer ground side of the 3 jaw chuck jaws gripping the ID of the sleeve as seen in the first photo. The clamping force here has to be snug but not have enough force to distort the thin sleeve. And therein lays a problem.

To face the end of the sleeve I took only shaving cuts of about 0.001" per pass due to the part projection and with the expectation that the sleeve would start to chatter and ring like a bell. It didn't with the extremely sharp tool bit used but suddenly, without warning, the sleeve flew out of the chuck jaws and right across the room! I thought, this is it, after all of the work done to date, a ruined distorted sleeve.

However, I somehow must have banished Murphy this time as the part behaved like a piece of spring steel, it was undamaged save for a few minor dings on both ends of the sleeve which would be machined away.

Now, how to solve this problem.

Set the sleeve back in the chuck jaws as before, tighten them a little bit more, and take 3-5 shaving cuts. Stop the lathe, check and retighten the chuck jaws if necessary. Repeat this cycle ad infinitum. Now, there was no more drama and the sleeve was finished to length reversing the sleeve part way to remove all of the ding marks. Probably, the slightly tighter chuck jaw grip did distort the sleeve a bit but it reverted to circular again when the jaw pressure was removed as the sleeve still fit perfectly in the bore of the right angle attachment and on the quill of the mill after it was trimmed to length.

Live and learn.

to be continued.

[rmac]

Now, how to solve this problem.

Anybody else thinking "soft jaws"???

-- Russell Mac

[Bill Shields]

Or spider?

[neanderman]

Doesn't the sleeve need a compression slit so that it can clamp on the quill when the attachment is tightened down?

[Carrdo]

Ed, as I noted, "to be continued".

A spider and soft jaws may be the answer also but I haven't investigated these alternatives as I got away with what I described. Will keep this in mind for the future.

[Harold_V]

It would have been simple to have just parted the piece when you were satisfied with the diameters. A thin and sharp parting tool would have ensured successful parting. It's much harder to move a piece when machining near the jaws as opposed to taking a facing cut on the extended end, as in this instance.

H

[neanderman]

Ed, as I noted, "to be continued".

Forgive me. I thought I might be putting the cart before the horse, but wanted to be sure this aspect was addressed.