Machining Cast Iron?

[old martParticipant @oldmart]

I bought a 4" steel backplate on ebay with the 1 3/4" x 8W thread for Smart & Brown, it got fitted in the centre of a faceplate, and works fine, although I always keep the spindle end lightly lubricated. All the others except the opener for male stepped collets have been made in CI. I have bought backplates with the 1 1/2" Boxford thread to rework to S & B size as long as the boss diameter is nice and thick. It saves a lot of machining mess.

[Bo’sunParticipant @bosun58570]

Posted by Nigel Graham 2 on 02/11/2020 18:30:52:

Bo'sun:

I don't machine cast-iron very often but when I do, I use moderate to low speeds. That helps control the mess!

Cast-iron is often used for machine parts because it has a better vibration-damping quality than mild-steel.

Yes you could use mild-steel for a back-plate, as far as I can see, and I dare say some do. After all it is not very large and is heavily clamped so not very likely to ring.

If you are prepared to machine a casting but would prefer steel to iron then you may as well buy a sawn slice of free-cutting mild steel. As you say, buying it ready-machined would put the price up but more significantly a back-plate is normally finish-turned to match the lathe and chuck anyway.

Good morning Nigel,

Having a back plate that matched the lathe and collet chuck would be great, but for whatever reason, Warco supply the back plate to suit the lathe, but it needs machining to suit the Collet Chuck. No doubt they would say it gives you the choice to use any Collet Chuck.

[Bo’sunParticipant @bosun58570]

Posted by Dennis Pataki on 02/11/2020 21:44:48:

Bo'sun, I'm thinking concentricity. Not familiar with your particular project, but if part is machined mounted on the lathe spindle for which it is intended, concentricity is pretty much assured.

Regarding material, free cutting mild steel might be a good choice too.

Hi Dennis,

Very pleased with the result. 0.006mm TIR on the tapered bore of the ER32 Collet Chuck. I think much of it was probably luck.

[Nigel McBurney 1Participant @nigelmcburney1]

Cast iron has always been used for backplates,probably since chucks as we know them were invented,most backplates have a smaller diameter boss to contain the thread plus a lot thinner larger diameter to take the chuck,so if a steel sawn blank is used a lot of material ends up in swarf whereas with a cast backplate there is little material waste,cast iron was also cheaper to produce ,and there were lots of foundries in this country.Steel was more expensive as there were far fewer sources of manufacture.And in the days of carbon steel tooling and HSS tooling it was easier and quicker to produce components in cast iron,just think about it threr were no HSS hacksaw blades to cut off thousands of backplates ,Think how long it would take to cut off the blank for a 12 inch chuck.The ability of cast iron to absorb vibration may have been effective on very large backplates ,but on our small machines I would think that the material may not matter though having worked a lot with cast iron I would think that the steel spindle with a cast b/plate is less liable to "stick".Nowadays with fewer foundries ,availability of mild steel with short leadtimes .high speed manufacture with CNC and new cutter material ,for smaller batches of say 4 or 5inch backplates for the hobby market there is probably little advantage of cast iron over steel. I like machining cast iron,did a lot during my apprenticeship,though if machine tols are not kept clean severe wear can occurr particularly in the days before hardened bedways were available, I have seen the bedways on a worn plano mill look like a piece of wood or chair leg that has been scatched for years by a cat,

[ADRIAN THOMPSON 3Participant @adrianthompson3]

Hi I am attempting to m/c a reeves casting of the Entablature for the M E Beam engine. The casting is so hard that it has chilled when casting. I have`nt come across this before so I tried to flycut the outside edge with a carbide insert tool. I have machined Stuart castings without any problems but with Reeves casting, sparks were flying all over the place. No chance of machining it so I have sent it back to Reeves for a replacement. I have a question to ask, Can the chilled iron be annealed making it softer, or is it scrap? Thanks Adrian

[JasonBModerator @jasonb]

Yes it can, you need to get it to 850-950 degrees C which is a bright orange and hold it there for about 1hr on that size casting and then let it cool as slowly as possible. If you have an open fire or woodburner put it in there and let it cook for the evening and leave in the ashes until morning.

Carbide will sometimes get through it but you are then stuffed if you want to do further drilling and tapping as the HSS wont

Edited By JasonB on 05/01/2022 20:23:33

[Neil WyattModerator @neilwyatt]

Posted by JasonB on 05/01/2022 20:16:39:

Yes it can, you need to get it to 850-950 degrees C which is a bright orange and hold it there for about 1hr on that size casting and then let it cool as slowly as possible. If you have an open fire or woodburner put it in there and let it cook for the evening and leave in the ashes until morning.

Carbide will sometimes get through it but you are then stuffed if you want to do further drilling and tapping as the HSS wont

Edited By JasonB on 05/01/2022 20:23:33

Take some care though. I overheated a flywheel and it ended up like a pretzel. For years it hung on the door of my old workshop as a warning against folly.

[SamsarandaParticipant @samsaranda]

Adrian

I have had a lot of problems with Reeves castings, some of the cast iron ones were so hard that a week in my woodburner had very little effect, whereas some it worked in “softening “ them. The quality of their castings is very variable, some of the cast iron ones contain shrinkage cracks once you machine off the outer skin and their gunmetal castings frequently contain inclusions. I managed to get around the problems with some of the cast iron problems by buying cast iron bar and machining from scratch and ended up with a much better component, not applicable if the casting is a complex shape. To overcome the problems I encountered with the gunmetal castings I bought bronze bar stock and again made from scratch. In a previous life I was a quality manager in an engineering company, I had to deal with foundries and the quality of the product that they shipped to us, once identified I expected them to resolve problems with their product, we produced product in cast iron, stainless steel and some of the more exotic stainless grades for the food and pharmaceutical industry. Dave W

[egaParticipant @ega]

I suppose it would be possible to finish machine a backplate from cast steel, thus avoiding the cost disadvantage in producing one from a solid billet. Again, a steel backplate could be fabricated by welding or even using adhesive.

[Bob Unitt 1Participant @bobunitt1]

Posted by Samsaranda on 06/01/2022 10:49:04:

Adrian

I have had a lot of problems with Reeves castings, some of the cast iron ones were so hard that a week in my woodburner had very little effect, whereas some it worked in “softening “ them. The quality of their castings is very variable, some of the cast iron ones contain shrinkage cracks once you machine off the outer skin and their gunmetal castings frequently contain inclusions.

I've had problems with my Reeves 'Lady Stephanie' castings, quality dropped alarmingly shortly before the old Reeves folded. I wonder if there's some old stock still being sold ?

[BazyleParticipant @bazyle]

Unless your woodburner is being overdriven to the point of damage to both it and the chimney I don't think it will get hot enough. I have never had any luck with bad castings in the woodburner even leaving them for a week and trying to move them to the hot parts (which they immediately sap the life out of .

[SamsarandaParticipant @samsaranda]

Bazyle

I found that small cast iron castings would improve after a couple of days in the log burner but for larger castings it was a waste of time, they were still as hard as glass and no tools would touch them. Dave W

[John ReeseParticipant @johnreese12848]

Cast iron works best with a neutral rake or negative rake tool. I suggest HSS so you can get a square corner at the spigot.

[John ReeseParticipant @johnreese12848]

Cast iron works best with a neutral rake or negative rake tool. I suggest HSS so you can get a square corner at the spigot.

[Author]

Posts