Turning a rectangular plate into a circular one

Opposite way to above piccies.

Cut the steel out and leave square ish it don't matter.

Drill and tap through largest high tensile long enough bolt you have, ie Hex head long enough to drop behind jaws and pull in to them when steel threaded on.
If drill straight through and bolt, most likely it will slip and or rotate no matter how tight.

Just simply turn o/d with a suitable carbide and wear a face helmet, arm and neck protection. Best carbide found to date for eccentric interrupted cuts are the Kennametal Top Notch bull nose or parting, virtually unbreakable.
At this point now have an external working edge.

Now if jobs on tight, dead simple remove the bolt with job and unscrew by hand.
Swap jaws over to external and slap job n and drill and bore the rest out, easy used to have to do it that way on a small lathe.

Holding off the bore will impregnate/deform.mark up more in to the job and have substantially reduced holding force than off outside. Done hundreds.

Well thanks you everyone for the replies.

i have done it & 3 points came up

1) Brian sweating reminded me that sitting on my shelf was an 80mm hole saw so I have cheated for now.

2) I did experiment on one piece turning from the face but grinding an HSS cutter with the right cutting profile was not successful & produced a lot of chatter, although I did get the radius clearance on the side OK. It did take a while & not really worth the effort. A bit like using a cut off blade.

3) I did like Jon's suggestion of tapping the centre & turning to size & that worked great. It pulled the piece square to the jaws & i was able to face the quite rusty piece as well & get tight to the stud with no slipping. However, his comment about turning off the corners is still a problem that I am contemplating. I take the advice about Kennametal tips. They must be better than my cheapo chinese tips but I do baulk at the price of the holders at £ 60+ each from MSC

Has anyone any comments as to how I can reduce the cost of holder ( 12mm) to enable me to use the better quality tip with the correct screw? I read on other forums that replacement screws for Kennametal tips can be an issue as they vary from tip batch to batch

Also which tip. Does it need to be thicker for an interrupted cut. Is CCMT OK as it can be used for other work

Edited By Sam Longley 1 on 09/09/2017 11:49:32

That's what I use, interrupted cut or not.

Andrew

You might be able to make your own tool holder, this one is for a 16 mm triangle without a hole and is made from a bit of car rear axle.

Ian S C

Any of our suppliers will do more cost effective holders in no particular order Glanze (via Chronos) ARC Eurotrade, RDG, JB Cutting tools mentioned above & Greenwood at a slightly higher price. I've got holders from all these companies and they do the job. JB also do kennametal, though not sure of full spec. If shopping at MSC check out the monthy discount flyer which can be found on their site and usually has tips at reduced costs.

Glad to have been of some use Sam.

Eccentric or interupted cuts usually create havoc with the normal recommended issue tools and tips.

I aquired two Kennametal NSR2020JK3 and 2525 back in 92 when we stopped doing the Carlton joints for the Coal Board, machines junked. I wouldnt want to know the price each but the main difference to quality is the rigidity. You could look at it tis way if a cheaper tool flexes and breaks a tip at £10 thats better spent on a better tool.
One of the NSR2020 i turned down with those NBR48R K68 or square 1/4"? wide parting NB4R K68 on an ML7 like butter. Rarely use nowadays but if eccentric or intermittant its the first of the tools i reach for.

The real way of comparng tools is having a like for like cheapy such as J&L own brand and others advertising on here to the real deal. Will find its chalk and cheese having learnt the hard way over the years.
In short the cheapies flex, remember paying £55 pus vat from J&L for an internal thread cutting tool, just came out ripped or with judder marks and could actually see the flex/vibration. Had to replace said item with a quality used jobby from Kenametal, 17 years later still using almost daily and was half the price of the J&L thing never used since.
Have similar instances with cheap own brands like Glanze, tried put back in box and left to rot at £100 ish a chuck, false economy.

Just bide your time with tooling dont get sucked in and wait for a bargain from a reputable brand, it dont matter what it looks like.
Have built up my arsenal mostly this way and two companies that stand out for me are PH Horne and Ceratizit, never had a mediocre tool or tip and top of my favourites. Seco, Iscar, Arno, Kennametal, Mitsubishi, Manchester proper brand names wont dissapoint if you will get the use out of them.

I've just had to do this for my Half Beam flywheel. First cut the square as near round on the band saw.:

Then fit to lathe. Mine is Chester Conquest. Which says maximum turning is 7" ie just over 177mm. This was only possible with the guard removed.

This has taken quite sometime and still needs the finishing touches.

Plasma cutter

Drill 4 holes in the hole centres

Cut 4 slightly oversized discs out in 5-7 mins with a jig

Edited By Ady1 on 07/03/2022 19:54:57