myford drilling of centre

[fcheslop]

I have a problem with my old ML7 and wonder if anybody has had the same. When drilling deep holes in small diameters the hole never drills true always comes out to one side and if the hole is very deep it can come out of the side of the job sorry if I'm not being very clear.The machine has recently had new bearings and mandrel fitted but the problem existed before and has not improved.Have set the machine up with a test bar between centres and clocked in using a test bare fitted into the headstock it will turn true and bore true but Will not drill true.I know I'm probably missing something simple but cant find it .The tailstock has been stripped and no burrs or any problems found in the casting or barrel.Its always done this since i purchased it but is now becoming a problem due to wanting to make ever smaller parts. The machine is mounted on a sturdy wooden bench that does tend to move with the change in humidity but I always set it up for doing accurate work and can turn 14 inches to within a couple of tenths 0.002 and bore to the same accuracy or as near as i can read my mikes scale.I withdraw the drill often when drilling but some times i think i see the drill bit dipping as it starts the smaller the dia the worse the problem I've also used different drill chucks?.My test bares where made on precision centre grinders and if i test between centres on the lathe there is no radial run out either at the head stock or tailstock Istill think it is something simple I'm missing but now have no hair left to pull out.Any help would be appreciated.
regards Frazer

 

[tel]

Sounds like the tailstock is out of alignment to me - put good clean centres in headstock and tailstock and see if you can nip a razor blade between 'em without it tilting

 

[Blogwitch]

How large are the drills you are using? and as Tel says, make sure you always start off with a good centre point.

If you are heavy handed, and don't 'peck' the holes out, you are just liable to end up with the drill almost coming out of the side of the job.

I can get away sometimes with putting a 1" drill thru, and not having it go off centre. Anything smaller, and I will always peck drill.


Bogs

 

[don-tucker]

What I did to check the tailstock was mount the dti on a bar in the headstock chuck and test around the tailstock barrel also with this setup you can check the barrel for being parallel.
Don

 

[fcheslop]

Thanks gents,Tel ill try that when i get of punishment duties[gardening] If the tailstock was out would it not machine a taper just a question
John the problem rears its ugly head below 3/16 and get worse, I'm currently trying to drill holes from no60 to 75 and at this size of hole you have to be careful as you know theres usually more swearing than cutting fluid.The lathe has always had this problem i bought it 30 years ago and it was made in 1965 and was only used in a scientific lab but may have been abused who knows.Just a little background i work/worked on precision cnc and robotic equipment and made the test bars on these grinders so i know they are accurate just so you know its not some hairy a-sed fitter trying to force a 3inch drill through some rough plate :big: but the problem is becoming a pain and I've seriously considered replacing it but it feels like putting the dog down and it cost £200 for the new headstock mandrel and bearings but maybe i should just cut my losses but i don't like giving up.I'm certain its got to be some thing daft I'm overlooking
Don, Thanks I will try your suggestion
Thanks again gents will update if/when the problem is found or sit there broken hearted :big:

 

[JimM]

I had/have a similar problem on my old Atlas lathe. I've managed to get it better than it was but I've tweaked so many things I'm not entirely sure what worked ! I suspect the problem was with the tailstock taper, I've given it a light ream and that seemed to make thing better, when I get a chance I'll try again and will report back

Cheers

Jim

 

[Jasonb]

Can you mount the drill chuck in the headstock and test it for run out? As you say its OK with a CTr in the tailstock it may be the drill chuck thats out.

Jason

 

[fcheslop]

Thanks, Jason ive already tested the chucks and they seem ok just spent the last couple of hours looking round again cant find anything obvious so going to completely strip it and start setting up from the begining its due a good clean up .
Jim hope the Atlas goes well.
regards frazer

 

[chipswarf]

A technique I've seen recommended has you start the hole undersize, then open to just the planned drill diameter with a boring tool, D-bit or end mill, to guarantee straightness and concentricity. This serves as a guide for the full diameter drill.

In older texts, it's often shown how to stabilize the entering drill bit by side loading it with something from the tool post, like a backward tool holder. If you orient the drill cutting lips, they can cut as a supported boring tool and give the same result.

Mark

 

[New_Guy]

it sounds like a very simple common problem your tailstock bore is worn you say the machine is 30 years old so its no surprise

as i understand it when you buy a new lathe the tailstock center should be a touch high this really wont have any effect on turning so its not noticeable and its so as you use the machine the center will slowly lower as the tailstock ram (quill) wears in the casting from gravity and the like i would bet my 2c that thats a factor in your problem unfortunately you cant fix it other than by boring out the casting making a new ram

have you thought of maybe making a sort of drilling/high speed drill tool for your cross slide? having the T slots would make a tool like that very handy and you can make sure its dead on it may help who knows

 

[Blogwitch]

NG,

unfortunately you cant fix it other than by boring out the casting making a new ram

Not quite correct, I rescued my Atlas tailstock which had a droop snoot.

http://www.homemodelenginemachinist.com/index.php?topic=2114.0


Bogs

 

[lordedmond]

you say ML7 and with your comment on the price for the new shaft and the bronze bearing that have replaced the soft shaft and babbitt I am assuming so

its the design of the tail stock you have the non ejecting one with the screw through the hand wheel they get sloppy , a ML7 super on will fit and will improve your problem . when you replaced the bearings did you replace the thrust bearing as well ?. I had the same problem but not as bad , I to replaced the bearings ect , gave up in the end and dropped a load of dosh £7K plus on a new blue job from my local supplier ( Myford ) only six mile down the road this one will drill correctly.the 1 inch bore on the mandrill is a joy . ;D

BTW a mate has fitted a super 7 TS to his 7 and his drill straight no problem
as a final point have you tried the Dormer PS point drills http://www.greenwood-tools.co.uk/ishop/728/shopscr81.html


Stuart

 

[fcheslop]

Thanks again,Food for thought i have started to make a mill/drill unit for the cross slide with a micro feed but am holding off finishing it until the lathe is working to my satisfaction.Thanks for the link Bogs.Stuart you are correct about the type of tail stock fitted but if i where to put 7k into messers Myfords hands although i would love to my personal financial adviser [Mrs H ] would remove some much loved delicate parts from my anatomy :big:
regards Frazer

 

[lordedmond]

You are thinking short term a new lathe will last you a lot longer after the other parts have ceased to function :big:


Hope you get it sorted the drill quoted do help a lot you will not believe how the drill no effort required , they will outlast the cheaper one by about 10 fold



Stuart

 

[New_Guy]

NG,

Not quite correct, I rescued my Atlas tailstock which had a droop snoot.

http://www.homemodelenginemachinist.com/index.php?topic=2114.0


Bogs

man thats a good idea it would sure be better than boring such a long hole and making a new ram lol i noticed it had a white lead hole how old was it? you wont get that use out of these new lathes lol

 

[fcheslop]

Well Gents, I have to hang my head in shame and go to the back of the class it is wear in the tailstock body 6thou at the front of the casting a repair is not possible at the moment so I will have to consider what to do either buy a new smaller machine or Waite until I'm In a position to re machine the body as per Johns article.Currently kicking myself for missing it in the first place [call youreself an engineer answer muppet] but the most important thing with the help of the forum it has been found and I sincerely thank all who took the time to reply.

 

[Blogwitch]

fcheslop,

Nothing to be ashamed about, sometimes you can't see the forest for all the trees that are in the way.

At least you have now found the cause, and at a later date, you can do a fix or if pennies allow, buy a replacement.

NG,

I never used the white lead pot, as invariably I used cutting paste when using a solid centre. Supposedly, as far as I could trace, the lathe was made sometime in the late 30's. as it came across the pond on the lease/lend contract, to help with the war effort.


Bogs

 

[don-tucker]

No need to "hang your head in shame" I went through all that and put the good guys on here through a lot of aggro to find it was a burr my son had kindly donated.
Don

 

[lordedmond]

Well Gents, I have to hang my head in shame and go to the back of the class it is wear in the tailstock body 6thou at the front of the casting a repair is not possible at the moment so I will have to consider what to do either buy a new smaller machine or Waite until I'm In a position to re machine the body as per Johns article.Currently kicking myself for missing it in the first place [call youreself an engineer answer muppet] but the most important thing with the help of the forum it has been found and I sincerely thank all who took the time to reply.

Glad you have found the root cause of the problem. I was going to suggest that you put your test bar in the tail stock and see where it points to

Just for info I have just come in from drilling a 5/32 hole in 316 SS 4 1/16 inches deep so deep I had to pull the tail stock back to clear the chips , result dead centre at the other end

If I where You I would keep my eyes open for a super 7 tail stock they are so much better

 

[fcheslop]

Hi Stuart. Going to have to consider the options 1 spend the money at Myford and loose some soft dangly bits
2 spent the kids inheritance with above consequences
3 repair my old banger more likely and less painful
4 find a good s/hand tailstock
5 find the combination to Mrs H purse this I know is impossible
Ive stripped and cleaned the lathe today and its in reasonable working order so will just have to plod on until an alternative becomes available was thinking of a new small lathe but after reading so many threads about alignment problems just not sure what to do but intend to have a look at Harrogate show to see whats available as my milling machine is now well past its best after 24 years of abuse having had all sorts from Honda CX500 motors to large lumps or steel milled on it.I think in the near future its simply going to be time to re invest in some new kit better than giving it to the bankers i suppose although a nice Thruxton Velo might sway me :big:thanks again