Home made Boring Bar. Advice needed.

[ventureoverland]

Morning all.

I'm after a bit of advice as I'm just starting out with my Hercus 260.

I want to make a boring bar with a HSS cutter.

In principle I'm thinking a 12mm or 16mm mild steel bar with a 3mm or 6mm hole cut through the end at 45 degrees to the work and a grub screw to hold the HSS in place (3mm and 6mm DIA HSS seems readily available on eBay).

I want to be able to bore down the length of the piece and then face the inside off with the same tool, hence my thinking 45 degrees to make grinding the HSS easier.

Questions.
1. Does the above (45 degree) bit sound feasible / practical or is there a better way?
2. I suspect i may need to bore a few inches deep and maybe 1 - 2 inches diameter. With this in mind what size bar and HSS would you recommend?

Any thought or ideas would be most welcomed.

Thx
Jon


Thx
Jon

[bollie7]

Jon
What you are suggesting is quite common. Usually there is a hole in either end of the bar, one at 45 deg as you suggest and the other at 90 deg.
If you decide to make one, the biggest dia bar you can get/have that will fit in your tool post and allow you to get into the job would be the best for rigidity. Personally I'd go for 6mm dia HSS in a bigger bar.. You will probably find you will eventually need an assortment of boring bars anyway.
Something else to consider. Broken centre drills, slot drills, end mills etc can be reground into boring bar bits.
If you make you bar from square it will be easier to hold in the tool holder but you can't rotate the bar to adjust the bit height, angles etc. If you make it from round bar you really need a holder that will clamp onto the bar to stop it from rotating. You can always put a flat on the bottom and clamp it directly in the tool holder but that sort of defeats the purpose of making it round in the first place.
At the end of the day there are really no "set in stone" rules for tools, boring bars etc. There are optimum tool angles etc for cutting various materials but how you hold the tool bit is really up to you. Rigidity is the key thing.
Ive done jobs where I've had to make a special boring bar up to get into that particular job and have welded a HSS bit to the end of a high tensile bolt etc.
Hope this helps
regards
bollie7

[Grahame Collins]

May I suggest using 12 or 16mm Grd 8 bolts of the appropriate length?
Known quality
Easy to source - nearest bolt shop
Rigid enough for the work,
Easy to turn, drill and tap
Relatively cheap

Grahame

[pipeclay]

A few more questions 1st.

What type of tool post do you have?

How big is the opening for your tool in the tool post?

Apart from the sizes you mentioned about your work pieces what will be the smallest diameter you will be boring?

When you talk about being able to face are you refering to be able to give a flat bottom to your bore or being able to back face with it?

[ventureoverland]

Wow. Thanks for the guidance & info.

I hadn't considered using bolts. I'll give that a go.

Pipeclay, when I said facing I meant give the bore a flat bottom (and a square corner).

With regards minimum diameter, my largest drill at the moment is a 16mm so I would need something that I could get into the 16mm hole and bore out from there (hence me thinking of a 12mm bar). As bollie7 suggested I may end up with more than one bar!

My tool holder currently is an old school one that will hold 4 tools and rotates and will accept a 16mm tall tool. Certainly is not a QCTP.


Thx
Jon

[Techo1]

There is no need to use a high tensile bolt, any bolt or piece of mild steel bar of a suitable diameter will do the same job.

Lex.

[pipeclay]

Going by your drill size I would suggest you may need at least three or four bars.

Seeing you have the 4 way post it might be easier for you to use either bright or black square bar,for the holding (tool post) section and turn the OD to suit.

It would seem that you would require a maximum 10mm OD bar if not 8mm for you smallest bore if enlarging from 16mm,you need to allow for swarf and trying to get to centre when facing.

[ventureoverland]

Mmmm. 3 or 4 bars... Mum always said practice makes perfect:)

I do have some 10x10 MS bar, may try and get to play over the weekend... That is if I don't get anymore blown over trees to clear up. Lost one last night.


Thx
Jon

[Oldneweng]

Mmmm. 3 or 4 bars... Mum always said practice makes perfect:)

I do have some 10x10 MS bar, may try and get to play over the weekend... That is if I don't get anymore blown over trees to clear up. Lost one last night.


Thx
Jon

As has already been mentioned , you can turn a boring bar on each end so you just spin it around for the next size. I have made one like that, but it gets very little use as I have 14 and16mm Seco indexable bars now that have covered everything I have needed to do. I have also ground a small drill bit to make a very small bar. The bit formed the whole bar.

Dean

[Bryan]

My favourite small bar is simply ground from a long piece of 3/8" square HSS. Something like that would be great to open your bore up enough to get something bigger in.

[ventureoverland]

Lots of good ideas and suggestions. That's guys. I'll let you know how I get on.


Thx
Jon