Boring tips - Importance of sequence II

Earlier this year I made up a bandsaw bracket that showed the benefit of using the right sequence. ( https://metalworkforums.com/f303/t20...tance-sequence )
This project does too, but also illustrates how it is sometimes easier to make multiple parts. At the various jobbing workshops I've been at, invariably when making a new part, the person doing the job will make up two or more parts. There are a couple of reasons this may be a good strategy -

• With most jobs of any complexity, equipment setup takes the time. If material costs are minor, you may as well do one or two more as the time taken for multiple parts may be next to nothing
• If a computer is involved (CNC) then usually if a part is to be made regularly, a trial part is required to 'prove the program'
• It's nice to have a spare (or two) in case you bugger one up
• Occasionally someone will wander up after the event with something like 'You know that part you made for X..., well, we need another one.'

The start of this build was me being stupid. I broke a boring tip holder for the Kaiser. In the post fracture kicking I gave myself, I worked out that because the hole for the HSS is offset to put the cutting edge closer to a neutral rake position, running it to turn the outside of a spigot meant that there was bugger all clearance on the back of the tool, so the forces resolved themselves. It was also one of those nagging things and I could not really settle to anything that might hint at needing the Kaiser to bore.
Attachment 380727
This was an original Swiss part, no longer made, so I was not happy. It was case hardened (which I was not going to worry about), but importantly you can see how the square hole is slightly off axis. That makes it tricky. To broach a hole at an angle through material is not as easy as going square; to have to do it on round stock harder still; off centre makes it quite nasty unless you have a plan.
There are two versions, a long holder and a short holder, and for each of those there is a 'bore' version and a 'spigot' version. So 4 off parts plus another 4 if Murphy just dropped around to see what I was doing.
The material I'm using is EN25, chosen because Eric gave me some (ie it was free). 55mm diameter and I needed to get it down to 16mm thick and at least double that wide.

Attachment 380726
Once I had a flat bar around 230mm long, I cut it in half, so I would get 4 pieces from each rectangular piece. The broach entry point was counterbored with a 3/8" cutter and then drilled with the broach pilot drill. The broach exit point was chamfered in a similar set up.
Attachment 380725 Attachment 380724
Prior to starting the broaching I had this.
Attachment 380723
Broaching was done in a Hydraulic press using two v blocks to support the work. By leaving the parts attached, I gained extra width to support the part and by keeping it square, I did not have the part trying to roll away. The parts are over width at this stage, but I marked them with an assumed centre line and then offset the holes for broaching towards the centre of the part.
Attachment 380722
Once broached, the parts were cut down the middle on the bandsaw and rounded up. The short tip will only be 40 odd mm long, so I left them paired with a long version for ease of chucking/ turning.
Attachment 380721
Once round I could then tap for the grub screw. I used some key steel to align the grub screw holes square to the HSS hole by supporting the key steel on the wings of a smaller V block, while the other end was in a smaller V (the perf sheet underneath is just to lift the level up). Finally with most operations complete, the 'pairs' were separated. The long ends (around 65mm long) were not a problem to hold in an ER40 collet chuck to turn the holding spigot but the short ones could not be held well in the collet. By using the newly liberated long pair in the other end of the collet, with light cuts, the job could be done (there would have been around 25mm held in the end. I had to get them really tight though and even then a couple of parts were scored when they slipped.
Attachment 380728 Attachment 380719
These are the (near) finished parts. The only thing to do is put a flat on the spigot for the grub screw, and to align that I'll use the key steel again. I may even engrave the sides with 'bore' and 'spigot' just so that if Murphy comes around to use the boring head again, there will be no excuses.
Attachment 380720

(And thanks to Eric for the material, as well as some grub screws)

Michael

Very well done Michael. The sequence of operation is way harder than the actual machining and normally also the make or break of the job.
Ummm, your broach. Did you make it or was it a purchase.

Phil

Purchased. I'm not that skilled.
(do you need to borrow it?)

Michael

Quote:

---

Originally Posted by Michael G

Purchased. I'm not that skilled.
(do you need to borrow it?)

Michael

---

Thanks Michael but I have a few here I may have to resurrect.

Phil
Attachment 380737

I never find your tips boring Michael. :D Nice photos!

Very nice work, well done. Thanks for sharing.

Neat stuff Michael. :2tsup:

I take it the opportunity for rotation to occur during broaching is the reason for using the rectangular material rather than round bar. As a possible alternative could round bar be rendered immobile by turning the spigot ( maybe overlength ) and cutting its flat and then clamping off the flat to provide registration and prevent rotation? Bear in mind I have never used a square broach.

Bob.

Round is difficult just because it may want to roll = puts a bow in the broach - broach may snap.
Would not matter if the broach was square, hex or what ever. One way to get round this might be to make up a split clamp, but for a limited run like this, a lot of effort. Another, as you have mentioned, is to put a flat on the end and clamp that. Here I took the opportunity to use the sequence of operations to my advantage.

Michael