Drill deep hole so on a lathe. I

I need to make a very long washer from 40mm mild steel, it is 160mm long and needs a 20mm hole through the centre.

Any tips on doing this? I'd like to keep the hole in the middle!

Should I drill from both ends or just one?

Chris,

40mm O.D and 20mm I.D. is a stock size for "Hollow Bar"

Beyond that ... we would need to know the accuracy required before anyone could give practical advice.

MichaelG.

Hi, I have the steel here and want to make it tomorrow ideally!

The hole needs to run central through the bar. Accuracy within 0.05 from centre would be nice!

I'd drill from both ends. It helps if you make sure that the drill has a good straight start so I would bore the hole, say 16mm diameter and then put a 16mm drill down as far as you can reach, then turn end for end and repeat. If you can't get your 40mm bar down the lathe spindle then I guess you will need to hold the bar centred in a fixed steady. If you can use e.g. an 18mm drill before the final 20mm then this will probably help as well.

That's the way I've just drilled a deep hole down a new spindle for my Flexispeed. OK, that was only 1/2" OD, 9/32" ID  but the principle and relative length of drill was much the same.

Actually, you could probably drill all the way from one end, 160mm is not terribly deep for a 20mm drill but again I would make sure it had a good start by boring first and then step drilling.

HTH

Rod

Edited By Roderick Jenkins on 10/09/2014 23:56:31

Thanks, it will fit in the spindle and the drill bit is long enough to do it in one go. I just wasn't sure how to go about it.

Hi Chris,

please bear in mind that the bar you are using may not be round or parallel so .05mm may not be achievable which ever way you do it.

Ifi were making this item and needed to get it as accurate as possible i would do it as follows and yes it is a bit long winded but ...

start of with the material a little oversize 2-3 mm or so would suffice.

Set up in a four jaw chuck and get it running as true as you can

centre drill then drill through to 17mm and bore to size or even better is to bore to a size a little under and ream.

for the best accuracy i would make up a mandrel and mount the piece on it so i can finish turn the OD concentric with the bore.

Another difficulty would be measuring the bore at the chuck end and this is why i would allow a few spring cuts or ream so the bore is parallel and round.

thats my version anyhow

Ian

I would drill it a few mm undersize and bore it to finish size from one end. But you would need to use a good fat solid boring bar. Say, 15mm diameter or so. Finishing cuts would need to be light and run through at the same setting a couple of times to get rid of any slight taper toward the rear end.

For your spec,the only option is to gundrill, then put it between centres and then turn the out side true to each end of the hole.

If you want to drill it, like above, predrill and bore for about 1.5 diameter long, in your case 20mm hole X 30mm deep. Then with a chisel point sharpened drill, 175 rpm at .05mm to .06mm feed per rev feedrate, about 8 to 10 mm per minute, and 2 to 3 mm per peck distance. This will give you as good a hole with a conventional drill as can be achieved. I just put the drill just straight down, no pre drilled smaller hole. Have the work piece setup with a steady to support the front . Then after drilling through 1/2 way do the same again from the other end.

Neil

What was the outcome and how did you go about the job?

Just curious.

Neil

Latest issue 4491 has an article about drilling deep holes

I have the latest model engineers workshop, but did not see any such article.

Neil

Neil

Jason is referring to Model Engineer magazine, not Model Engineers Workshop.

Nigel

I don't have access to that.

I forgot about this.

I used a spot drill 0.5mm undersize from both ends then reamed from both ends, slightly mismatch in middle but no problem really. Holes at each end were within 0.05mm and allowed a bar of the correct diameter to fit through. Holes were slightly oversize though due to tailstock not being perfect.