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| ALB:
Hi all, can anyone tell me what's wrong with my lathe(or me :bang:) I am trying to bore a 20mm od bore 30mm long for a wee project i am working on, But the bore is oval measuring 20.00mm < 20.08mm in dia i am not going in to heavy final cuts are around 0.10mm and i am finnishing with a few passes to get the spring out of the boring bar which has a 8mm shank i have tried honing the bore but no joy it's a hobbymat md65 lathe I am using with a glanze 8mm boring bar and new tips. any ideas? James |
| Jasonb:
Once you get an oval an indexable tip with fine cuts will just rub and follow the oval. Change for as rigid a bar as you can get in your toolpost and use a HSS bit with fine depth of cut and keep the edge sharp Jason PS whats the material? |
| Bogstandard:
James, How thick are the walls of the cylinder? The reason I ask this is that if the part you are boring is held within the vice jaws, and they are on the thinnish size, then the walls can be pushed inwards by the chucks jaws. Then after boring, when the part is taken out, the walls then go back to their original positions and you will find the bore can be all sorts of shapes and sizes, out of round. If you are boring anything smallish, then it should really be done on material that is not being held within the jaws, but actually outside of the jaws, and then parted off afterwards. The same can happen in a collet chuck if tightened up too much, you bore to size, then when pressure is released, the hole is slightly oversized. Just something you might need to check on. Bogs |
| ALB:
Thanks guys Jason, The material is just mild steel EN1A i have a old brazed tip boring bar but again it's just 8mm i can't use anything larger but i will give it a good sharpen and try it Bogs, The wall is 8mm thk i usualy just nip up the jaws and try not to over tighten as it is just a 80mm chuck I never thought about using a longer part to hold in the chuck Thanks Thanks again lads :thumbup: James |
| BillTodd:
I think Bogs is spot-on with the chuck distortion diagnosis :thumbup: You might try making yourself a simple pot-chuck from a thicker piece of steel: bore it to the OD of your cylinder. (Mark it so that it'll go back in the chuck the same place) then slit it along its length to allow it to grip your cylinder. Bill |
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