Bars for Boring Head

This topic has 6 replies, 5 voices, and was last updated 6 March 2017 at 17:42 by Clive Foster.

Viewing 7 posts - 1 through 7 (of 7 total)

Author

Posts
5 March 2017 at 17:12 #287258
Iain Downs
Participant
@iaindowns78295
A while back i got a boring head for Xmas (my sister felt it very appropriate).

I've used it a few times, but I seem to have trouble with the bars.

These have 12mm round shanks and came in a set of 9 (from glosester tools, I think).

I've only used the shorter ones as my mill (CMD10) travel is only 30mm at most and anything longer would only reduce rigidity (which is not there in large quantities at the best of times).

What I seem to find is that the bar ends up with end end rubbing against the cylinder I'm cutting rather than the carbide tip cutting. This seems to get worse as the radius of the cut increases, though I'm noticing this after the bore is finished and not whilst it happens, so I'm not really sure.

There is a huge amount of spring in the system. I reckon that the bore is being undercut by 0.5mm or more. Obviously taking a number of cuts improves this, but I'm struggling to bore to size. It seems to measure OK when in the mill, but be bigger when I get it out. I expect this is dumb operator syndrome, but…

I'm typically boring out a 10mm hole to around 20mm (and about 25mm deep at most) so I'm not attempting anything terribly difficult.

At least one of the bars is now unusable – the tip has actually bent back – and the second is a bit dubious.

Apart from seeking expert advice, I'd also like to buy some more bars, but I only seem to be able to find either long bars for a lather or the sets of 9 which I'm not too happy with (usually coming with a head).

Assistance, advice and rude comments all welcome!

Iain
Advert

5 March 2017 at 17:12 #8597
Iain Downs
Participant
@iaindowns78295
5 March 2017 at 17:28 #287266
JasonB
Moderator
@jasonb
I would suggest grinding some more clearance on the bars that you have so that they don't rub, rather than have the non cutting part rounded as most of these cutters do grind it straight. You should easily be able to do 10mm holes with these without rubbing, I can with my set of 9. Clearance should get better as the hole dia increases so you may not have the tool held at the right angle to start with.

I mostly use bars which take a carbide tip, these have the advantage of a flat that the grub screw bears on and that gives you the correct position for the bar. Mine are 1/2" from Chronos but RDG look to do similar in 12mm shank, these won't go much below a 12mm hole so you will have to drill out a bit larger first.

Edited By JasonB on 05/03/2017 17:29:18
5 March 2017 at 19:45 #287296
Neil Wyatt
Moderator
@neilwyatt
As supplied, you pretty much have to set the boring bars with no top rake at all to avoid rubbing.

If you grind clearance underneath the cutting edge (like a lathe mounted boring bar would usually have) you can have some top rake and get freer cutting.

Bending it is provably a combination of rubbing and excessive depth of cut.

Neil
5 March 2017 at 21:30 #287311
ronan walsh
Participant
@ronanwalsh98054
There is a good video on youtube about far eastern boring bars. The chap in the vid recommends you change any of the screws on the head, and replace them with good ones. Also the brazed boring bars that come with the heads either need binning or grinding. The basic heads are ok, its the rubbishy accessories that let them down.
6 March 2017 at 17:10 #287488
Iain Downs
Participant
@iaindowns78295
Hi, Jason – thanks for the link.

That one appears to be about the right size. The two smallest in my set are 60mm (which is now bent – too much brutality according to Neil) and 80mm. So that is a good match.

However, I think I will try and grind some clearance on my current 80mm bar whilst saving up for the indexable one.

Iain
6 March 2017 at 17:42 #287490
Clive Foster
Participant
@clivefoster55965
If you have CAD its worth doing some hole'n tool shape end on view drawings at large scale to get a feel for the shape of tool needed to preserve clearances. Especially for small holes.

Clive
Author

Posts