|Nick Welburn||30/08/2021 20:01:28|
|81 forum posts|
So I’ve finished my 10v, I’m now building a cringle model engineering boiler. To do this I need to turn down a large ally casting. It’s too big and irregular for my 4 jaw.
|Jeff Dayman||30/08/2021 20:16:03|
|2176 forum posts|
you might try a plywood faceplate made in your own shop and mounted in a 3 or 4 jaw chuck. This plywood faceplate is just a small disk and a larger disk of 3/4" / 19 mm thick plywood sawed out and glued and screwed together. The parts to be machined are screwed directly to the larger plywood disk. If the assembly is mounted in a 4 jaw it can be zeroed where desired and no extreme accuracy line up of part to plywood is needed. If using a three jaw to hold the plywood faceplate some care will be needed to align the part to the disk. I sometimes make a centre pop or small hole where zero needs to be, use the tailstock centre to locate on this mark or hole and hold the work to the disk while screws are driven to secure the work to the larger disk.
Light cuts are a must with this setup.
Cheap as chips and it works. Some pics of a couple of mine are in the August EIM magazine in the letters section FYI.
|Nick Welburn||30/08/2021 20:28:36|
|81 forum posts|
Ok it seems my language is incorrect
I have a face plate. This is currently mounted on the backplate.
How do I safely mount stuff to a face plate?
21431 forum posts
Have a look at Cringle's thread over on HMEM forum, you can see how he holds it there. The clamps with a jacking screw are a bit less likely to go flying than the stepped packing blocks.
Or if you drill the 4 foot holes you could then screw to a wooden plate like Jeff describes.
|Andrew Johnston||30/08/2021 20:39:28|
6263 forum posts
Nothing wrong with normal clamps and blocks, or anything else for that matter, provided the setup is thought through in terms of what might move under cutting forces. You'll not be running fast, no more than low hundreds of rpm. Here are some examples:
|Nick Welburn||30/08/2021 20:47:15|
|81 forum posts|
That’s an awesome thread and a whole new forum to consume
cheers I can make a set of those clamps. Is it the done thing to drill and tap the face plate or do big boys manage with the existing holes?
|Andrew Johnston||30/08/2021 22:13:42|
6263 forum posts
Definitely not, large faceplates are not cheap! I use existing slots, but if needed I'll make a smaller plate, or block, to hold the part:
|391 forum posts|
I have a normal backplate as in the photos posted by others, but also have a backplate intended for wood-turning. It is a blank disc with an array of small holes in it, a bit like that in a dividing head but symmetrical. It is great for odd shapes that can't be easily attached using the normal slots. The holes are only big enough to take M4 bolts but enough of them can be fitted to make it safe for low speed work.
|John Olsen||31/08/2021 06:43:57|
|1196 forum posts|
Figuring out how to hold things can sometimes be a quite major part of the art of machining. Quite often the thinking and planning part takes longer than actually mounting the part, which then takes longer than the actual machining.
I've used sacrificial layers added onto the faceplate quite often. These can be plywood, or if you want a more accurate thickness, a piece of aluminium, which I prefer. They can be held on in various ways, depending on whether or not your faceplate has T slots or through slots. Whatever holds the extra piece on has to either be clear of where the job needs to sit, or flush with the surface, eg using countersunk fasteners. With an aluminium plate, you can tap holes into it to hold the job to it. You do need enough thickness to allow this.
The beauty of mounting things on the faceplate is that it allows jobs that are much closer to the theoretical limits of the machine than chucks do. This is useful for those of us with smaller machines than we would like, which is probably most of us. I was able to bore a three inch bore HP cylinder on my Myford, the furthest out part of the casting was clearing the bed by about an eighth of an inch.
21431 forum posts
If you do make some clamps like the ones Cringle shows then either slot them for the stud or make then so that the distance from stud to jacking screw is longer than the distance from work to jacking screw as this ensures you get more clamping force where it is needed. Also put the bolt/screw head against the faceplate having turned off any code numbers first as it's less likely to mark the faceplate. One thing I did do on mine was to drill the mounting stud holes all the way through and tap them, so you het a few extra options for fixings.
Although I have used both this type of clamp and the stepped block type on the lathe the ones with jack screws are safer of things come loose as they will all stay attached to the faceplate unlike the step blocks that could fly off. I also find them a bit easier when setting up on the vertical face of the faceplate as the blocks can drop! always worth having a board on the lathe bed when setting up work on the faceplate.
One of the problems with smaller lathes of the imported variety is that the flange mount that they use means the slots can't extend that far towards the centre so either a separate plate to fix to the faceplate with CSK screws or for a job like this ply or MDF would work as it's only a small cut on a 65mm dia aluminium part.
The part in question from Cringle's thread
|Mike Hurley||31/08/2021 09:55:34|
|185 forum posts|
Nick, get hold of a copy of Tubal Cain's ' workholding in the lathe ', part of the Workshop Practice series. Quite cheap for the amount of info it contains, and will give you all mannner of sensible, practical and safe methods. Highly recommended.
|Nigel McBurney 1||31/08/2021 10:12:55|
918 forum posts
I prefer Jasons type of clamp with a jacking screw which cannot fly off.Now if you have not used a face plate before,then there can be problems, Face plates are relatively thin and the work piece may be stiffer than the faceplate so over tightening of the clamps may distort the plate,when the work is mounted ,the work may be off set sowill need balancing,one of the photos shows change gears being used as balance weights,before switching on the lathe motor bring up the saddle and tool to the work and rotate the work by hand to ensure that it does not foul the saddle or tool holder,and where possible bring the tool up to where it will finish the cut and again check to see if the f/plate without fouling anything. then start using a very slow speed to see if the work rotates freely without spindle balance problems and increase the speed until it is just under the point where the lathe shakes, avoiding vibration is far more important than reaching the ideal cutting speed,if say when using HSS which has a cutting speed of around 80 ft per minute on cast iron it does not matter if the speed is below out of balance gives say a cutting speed of 50 fpmin it just takes longer to do the job,out of balance can cause problems such as out of roundness and damage to the lathe. It was lot easier for my generation who did apprentice ships and saw operations such as this carried out by more skilled workers,though I did see someone catch a clamp with the saddle and dump the work and clamps on the shop floor. I do not like like loose blocks under clamps , I prefer to use aluminium or steel blocks which have tapped holes so the block can be attached to the face plate via a bolt from the back. sub plate can be used with lots of tapped holes but they reduce the space available between the face plate and the gap in a gap bed lathe. If I want to skim say a brake disc,I have the table part from an old rotary table which has t slots and lots of tapped holes,this is held in the 4 jaw chuck and if the work has to be really parallel I give the old table a light skim ,have done a lot of brake discs and other parts on this fixture .
|575 forum posts|
Is it the done thing to drill and tap the faceplate?
My opinion, it’s your faceplate, do as you wish with it, the thing is a chunk of cast iron not a priceless family artefact, you will not affect the value of it. If you are really worried about drilling it try putting a sacrificial plate on the front of it, bolted through the existing slots.
|Howard Lewis||31/08/2021 13:04:54|
|5298 forum posts|
When you clamp work to the Faceplate, just be careful not to overtighten the fastenings.
the fastenings only need to be just tight enough to prevent the work moving under cutting loads.
Too tight could cause distortion which destroys the accuracy of centering / locating, and in the worst case scenario, crack the Faceplate.
A small fastener can exert quite a load. I once cracked a Myford ML7 Cross Slide by overtightening a 1/4 BSF nut (M6 for those metricated )
104 forum posts
I have seen faceplates that look like a swiss cheese with holes all over which will put the plate out of balance at least, and weaken it significantly at worst. One solution I have often used to the awkward shapes/jobs with holes in inconvenient places problem is to bolt an old brake disc to your faceplate, once you've given that a light skim it will run true and you can drill holes anywhere, even weld brackets to it if necessary- brake discs are made from Meehanite which welds OK with MIG, never tried any other process for this.
You can see a brake disc being used in this photo.
If you don't have any old brake discs, your local garage will probably fish you several out of the bin for a small donation to their tea club.
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