Best machining process

[Howard LewisParticipant @howardlewis46836]

If the raw material is 75 x 80 x 12, by the time that it has been faced, it won't be 12 mm thick.

By working from corner to corner, the centre point can be found.

Assuming that your 4 jaw can accommodate the 75 x 80 mount it and face one side.

Note the comments about using sharp tools, correctly set,. to minimise risk of work hardening.

Centre drill

Drill

Bore to a suitable size, < 25 mm.

Turn up an arbor size and size with the bored hole. (Centre drill the arbor ready for later )

This would be a good time to saw off the as much of the corners as possible.

Mount the stainless on the arbor, machined face to the shoulder on the arbor. Loctite for added security?

Mount in the 4 jaw, and centre accurately. Use the Two Centres method.

Machine the outer to produce the 75 mm diameter.. Being an interrupted cut, take things gently!

You can use the arbor as a chucking piece to drill and tap for the M5 grubscrew. Drill through at 4.20 mm

Open up the outer hole to 5.5 mm x 15 – 20 mm deep.(20mm will leave 5mm of thread )

Tap the M5 thread.

Deburr the bore.

Hopefully, job done.

HTH

Howard

[Rowan Sylvester-BradleyParticipant @rowansylvester-bradley37244]

Thank you for all that hepful advice. It sounds like the "treppanning" process is not going to work, or is going to prove troublesome and difficult. Although I see that you can buy special "face grooving" tools for this (e.g. https://www.sandvik.coromant.com/en-gb/products/pages/face-grooving-tools.aspx). Does anyone have any epxerience using these?

So my process now (based closely on JasonB's suggestions) is:
1. Cut the stainles steel rectangle to a rough circle using a hacksaw. Whether this just means cutting off the 4 corners, or doing more cutting probably depends on whether I can reassemble and get working my power hacksaw.
2. Grip it in the 4-jaw chuck, and cut the outer 6mm to 76mm dia using an HSS tool.
3. Reverse it in the chuck (maybe change to the 3-jaw) and cut the other 6mm to 76mm dia.
4. Still holding it in the chuck, drill and bore the 25mm hole.
5. Hold by the hole in the three jaw chuck with the internal jaws and turn the outside circumference to 75mm dia.
5. Face both sides and the circumference.
6. Drill and tap the radial hole. I understand that I can't tap 25mm deep. I was thinking of just tapping it as deep as I could, and then "extending" the grub screw with a rod say 4mm dia ground to a conical point. This can just be loose inside the hole.
7. Finish with emery or similar. Make a 25mm arbour if necessary to protect my fingers

Other issues. If 304 is not the best grade to use, what is best? Yes, it does need to be stainless.
Yes, what I have is a piece of 12mm x 75mm bar. I know that facing it will end up with it less than 12mm thick. I was just going to take off enough to get a flat surface. The eventual thickness is not very critical.

Thank you – Rowan

[old martParticipant @oldmart]

I am confused by the metal description. 75 x 80 x12 mm BAR?

[JasonBModerator @jasonb]

Does it need facing, Plenty of flat and round bar used as is and finished with a "brushed stainless" look straight onto the mill surface which sounds like to look the OP is after

It's certainly the way most architectural stainless fabrications are done such as handrails, brackets, furniture, etc.

[old martParticipant @oldmart]

If it is flat plate, I would produce the bore first and make an arbor to hold it, as already mentioned. When it is on the arbor, just touch a tool tip against the side to make a mark slightly bigger than the finished diameter and remove it from the arbor and hacksaw just outside the mark for a rough diameter. Then refit to the arbor and turn the OD. The dimensions mentioned leave no allowance for finished size or thickness.

[Anonymous]

Posted by Rowan Sylvester-Bradley on 11/09/2022 15:41:28:

Other issues. If 304 is not the best grade to use, what is best? Yes, it does need to be stainless.
Yes, what I have is a piece of 12mm x 75mm bar. I know that facing it will end up with it less than 12mm thick. I was just going to take off enough to get a flat surface. The eventual thickness is not very critical.

Thank you – Rowan

303 stainless is the best/easiest to machine, doesn't work/heat harden easily. 304 is a pain the only real advantage it has is weldability which you don't need.

[JasonBModerator @jasonb]

Posted by old mart on 11/09/2022 15:43:05:

I am confused by the metal description. 75 x 80 x12 mm BAR?

As I said earlier 75 x 12 is a stock size flat bar in stainless, cut to 80mm long

303 is easier to come by in round bar rather than flat bar or plate so also as mentioned earlier get a piece cut to say 15mm long from 3" (76mm) dia round bar and you will have enough metal to machine to the exact size of 75mm dia x 12mm thick. Someone like M-machine will be able to supply that.

Edited By JasonB on 11/09/2022 18:06:43

[Martin Rock-EvansParticipant @martinrock-evans77799]

As a thought to the difficulties of tapping the deep hole for the grub screw, why not drill full depth tapping size, then only tap the first 7-10mm, just deep enough for the grub screw to be below outer surface. then use a small brass rod to make up the difference in depth. This way you don't need to tap the stainless so far. Brass will also help prevent scuffing the shaft it is going onto.

[Rowan Sylvester-BradleyParticipant @rowansylvester-bradley37244]

Thank you for all that hepful advice. It sounds like the "treppanning" process is not going to work, or is going to prove troublesome and difficult. Although I see that you can buy special "face grooving" tools for this (e.g. https://www.sandvik.coromant.com/en-gb/products/pages/face-grooving-tools.aspx). Does anyone have any epxerience using these?

So my process now (based closely on JasonB's suggestions) is:
1. Cut the stainles steel rectangle to a rough circle using a hacksaw. Whether this just means cutting off the 4 corners, or doing more cutting probably depends on whether I can reassemble and get working my power hacksaw.
2. Grip it in the 4-jaw chuck, and cut the outer 6mm to 76mm dia using an HSS tool.
3. Reverse it in the chuck (maybe change to the 3-jaw) and cut the other 6mm to 76mm dia.
4. Still holding it in the chuck, drill and bore the 25mm hole.
5. Hold by the hole in the three jaw chuck with the internal jaws and turn the outside circumference to 75mm dia.
5. Face both sides and the circumference.
6. Drill and tap the radial hole. I understand that I can't tap 25mm deep. I was thinking of just tapping it as deep as I could, and then "extending" the grub screw with a rod say 4mm dia ground to a conical point. This can just be loose inside the hole.
7. Finish with emery or similar. Make a 25mm arbour if necessary to protect my fingers

Other issues. If 304 is not the best grade to use, what is best? Yes, it does need to be stainless.
Yes, what I have is an 80mm long piece of 12mm x 75mm bar. I know that facing it will end up with it less than 12mm thick. I was just going to take off enough to get a flat surface. The eventual thickness is not very critical.

Thank you – Rowan

[old martParticipant @oldmart]

Plate is flat like a wall, and bar is cylindrical like a tree trunk.

[Rowan Sylvester-BradleyParticipant @rowansylvester-bradley37244]

The process that Martin suggested is almost exactly what I was thinking of (except that I was going to use steel rod rather than brass – I'm not too concerned about marking the shaft).

Thanks – Rowan

[Rowan Sylvester-BradleyParticipant @rowansylvester-bradley37244]

Posted by old mart on 12/09/2022 14:26:23:

Plate is flat like a wall, and bar is cylindrical like a tree trunk.

According to Google many suppliers use the term "bar" to mean a flat fairly narrow strip. Anyway, that's what I meant.

Thanks – Rowan

[duncan webster 1Participant @duncanwebster1]

I used Jason's method to turn the flywheel or a ST engine, but I took it right down to finished size from the start. Saw the corners off (or angle grinder), grip in 4 jaw, set face to run true, turn half length of OD and bore the centre. Turn round in 4 jaw, set face and bore true, finish turn OD. A 4 jaw is much better for this kind of thing, it gets a much better grip for one thing. Gripping a rough sawn lump in a 3 jaw is chuck abuse. You can't see the join on my flywheels. If the OD has to be dead on then finish on a mandrel, but that is something else to make and it doesn't help rigidity.

If using angle grinder be sure to wear PPE and make sure the lump is well clamped down. The only time I managed to inflict a minor injury with an angle grinder they rushed me to the front at A&E as soon as I mentioned how it happened, they see very severe injuries. As it was I only had a deepish cut caused by picking the piece up without gloves before I'd deburred it

[HuubParticipant @huub]

Other issues. If 304 is not the best grade to use, what is best? Yes, it does need to be stainless.

I have only machined 304 on my (CNC) lathe and it took some time to get the job done properly.

From what I have read on the internet, 303 is better for machining on a manual lathe. 304 is more corrosion protective.
The 400 series are easier to machine but are not as "stainless" as the 300 series
The L (leaded) series 304L, etc are better for welding.

I would go for 416 or 304.
You need sharp tools. If you use HSS tools, resharpen them often.

 

Edited By Huub on 12/09/2022 15:00:42

[JasonBModerator @jasonb]

Posted by old mart on 12/09/2022 14:26:23:

Plate is flat like a wall, and bar is cylindrical like a tree trunk.

So what do you call a length of rectanglular section?

Most people would use "flat bar" or "#x# bar" or just "flat" and would not call it plate

[Author]

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