Boring large bar on lathe.

[Chris DentonParticipant @chrisdenton53037]

Evening, I need to bore a 55mm aluminium bar on my lathe, it is circa 300mm long. It won't fit through the chuck so can only be held on the end in the jaws. I need to drill it to circa 25mm then bore to make a nice finish, then each end is bored to take a 28mm bearing.

I could do it on the milling maching but we've fallen out. And I'd rather do it on the lathe.

Any ideas?

[Chris DentonParticipant @chrisdenton53037]

[JasonBModerator @jasonb]

Hold one end in the 3 jaw chuck and support the other with a fixed steady. You will most likely have to come at it from both ends so softjaws or 4-jaw would give that little bit more accuracy.

Edited By JasonB on 01/06/2014 08:06:46

[Tony RayParticipant @tonyray65007]

Chis,

A fixed steady is the solution but depending on your lathe they can be rare and expensive to obtain but are essential for this type of job. One option is to fabricate one – there have been a few articles in MEW. I did make one successfully in wood 50 mm thick to give good support. I used maple but any close grained wood will do. I tapped it direct to hold some studs and used t nut for others. It was one piece and slid on to the job.

There are several ways to make the fingers but if you can use you mill it's probably a good method.

Do persevere with your mill, I find turning comes more naturally but milling takes more time to set up and is much less forgiving. Post your milling woes and someone will advise.

Failing all this perhaps there is some one local to you who could bore it for you ?

Good luck

Tony

[Ady1Participant @ady1]

Thats a big one on many hobby lathes

I would hunt down a prop shaft bearing and use a wooden steady with it

Jam the end of the workpiece into the bearing and support it in a fabricated steady

[StovepipeParticipant @stovepipe]

As a muddle-engineer trying to turn a large bar on a Cowells lathe, this thread is very useful, Thanks fellas, !

Dennis

[Chris DentonParticipant @chrisdenton53037]

I don't have a fixed steady I'm afraid.

I looked at my 9" four jaw chuck and has jaws that stick out a lot further and they are concave so it holds it very steady with no other support. So I'll give it a go, very slowly!

[Ady1Participant @ady1]

Will likely end in tears if you take that route. Around the centreline you may be fine but once you start moving into boring away from the centreline it's going to generate too much leverage

[John Stevenson 1Participant @johnstevenson1]

Don't do it at 300mm long without support or you will be wearing it.

If you do you will have to change your sign on name from Chris Denton to Pokus Nosus

Do you have a boring head off your mill that will fit the tailstock of your lathe ?

If so use that to bore with and make a steady out of two half caps of wood screwed together and fastened to a dummy tool. The position can be adjusted by using the cross slide and tool high adjustment.

[JasonBModerator @jasonb]

Along similar lines to JS's suggestion. Make a split wooden block that can hold the bar to the cross slide by boring it out in position. You can then drill and bore one end, flip it round drill from the other end and if you want a better finish along the length use a between ctrs bar, finally do the other bearing recess. You will want a long bed length for this.

[Chris DentonParticipant @chrisdenton53037]

Well…I tried it anyway as the 4-jaw held it very steady. It's very similar to the picture that JasonB posted.

I drill it out to 25mm, but only bored the end to take bearings to 27.96mm. It was fine, although the 4 jaw marked it quite badly so I had to turn it between large centres again.

From memory rpm was 155, very slow feed and 0.4mm cut depth.

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