Author Topic: Drilling around the circumference without RT (Read 18810 times)

raynerd · « **on:** July 08, 2009, 06:08:35 AM »

Hi, I was wondering if anyone could lend me some advice regarding drilling holes around the circumference of a bar without a RT.

I have a 1.5" bar and I wish to accurately drill three holes along 1" circumference at 120deg divisions. Clearly this would not be a problem with a RT or dividing head but I don`t have either and I am not in a position at this moment to purchase one.

My plan would be to accurately scribe the desired circumference using a fine point tool in the lathe, pop a hole somewhere along the circumference and then simply get a pair of dividers and trial and error move them from the point in two steps along the circumference until they return exactly back to the spot. Once I have got the desired position - mark and pop the remaining two points.

Alternatively there is a method of setting up a jig but my concern there is that the holes will only be as accurate as the jig and therefore in my opinion there would be less error in marking the divisions directly onto the work?

Any advice appreciated - I know a RT would be ideal but I`m sure there must be methods of doing this accurately without?

Chris

Darren · « **Reply #1 on:** July 08, 2009, 06:09:54 AM »

Have you got any hex bar?

raynerd · « **Reply #2 on:** July 08, 2009, 06:13:51 AM »

I do - I have quite a large brass or bronze hex bar that is about 1" across and I`ve never cut into (picked it up from the scrap about a month ago) and then some much smaller ally that I picked up yesterday. What are you thinking ....?

Chris

Darren · « **Reply #3 on:** July 08, 2009, 06:15:03 AM »

Hex has six sides, use every other two and you have your 120deg.....

I'm sure you can think of a way of using that info....

raynerd · « **Reply #4 on:** July 08, 2009, 06:24:43 AM »

Now that is food for thought!

It is a pitty - I`ve just spent £20 on materials but I could have used hex, marked and drilled and then turned it down to round. Perhaps I could use the hex I have as a jig - then I know the holes or marking on the jig will be accurate but that is providing the hex sides are true. Interesting but again, do you think this will be more accurate than marking out and drilling as I suggested?

Chris

Darren · « **Reply #5 on:** July 08, 2009, 06:28:49 AM »

Quote from: craynerd on July 08, 2009, 06:24:43 AM

do you think this will be more accurate than marking out and drilling as I suggested?

Chris

Definitely !!

And a whole lot easier....

Here I'm using a hex to make six holes, but it could just have easily been 3.

sbwhart · « **Reply #6 on:** July 08, 2009, 06:36:53 AM »

You can also use a gear thats devisable by 3 :- 9, 12, 15, 18, 21, 24 etc etc

But Darrens suggestion of hex bar is probibly best/cheepest.

or you could buy one of these

http://www.arceurotrade.co.uk/Catalogue/Collets/5C-Fixtures

Stew

Darren · « **Reply #7 on:** July 08, 2009, 06:40:57 AM »

I'd like a spin indexer, I see someone converts them to take 5C collets....

Edit: or was it ER32?

DavesWimshurst · « **Reply #8 on:** July 08, 2009, 08:09:36 AM »

Chris,
You could also index off the jaws of your three jaw lathe chuck.
Use a level on each jaw in turn and scratch the desired area with that fine pointed scribe using the cross slide to move it. Level each jaw on the back side and you can get 6 spacings. Or you could use a spacer block to the lathe bed to index from the jaws:

Dave

raynerd · « **Reply #9 on:** July 08, 2009, 08:43:25 AM »

Thanks for all your ideas. A few more questions and comments.

Darren - just to clarify exactly what is in your picture: did you make that from hex - also is it a mandrel, so your work clamps up onto the mandrel and the hex has markings on, you align your work, screw up the nut and drill, release, re-align .... as so on?

Stew - thanks for the link but I`m trying to get away from buying more tooling for now - have spent enough for another month (holiday later this month!!). I could get a rotary table from RDG for £60 just can`t afford it right now.

DavesWimshurt - I really like that idea, I have a three jaw and simply locking the head stock up on each of the jaws of a three jaw would give me the correct division. However -

I noticed you have power to your tailstock drill to offset the drill and make the hole. My tailstock does not go off centre and obviously have no power. I could possibly make something similar for the mill with the chuck facing up.....

Well I`m getting closer to having an idea how to do this..... Darrens mandrel seems a good idea also but again it would have to be vertical as I am drilling into the bar face rather than outside....

raynerd · « **Reply #10 on:** July 08, 2009, 10:19:06 AM »

A rotary table looks very desirable ...

... am I being defeatist?!

, I just need these hole bang on and it seems a useful piece of kit to have anyway!

Darren · « **Reply #11 on:** July 08, 2009, 12:21:09 PM »

In my pic it's what Stu pointed out

http://www.arceurotrade.co.uk/Catalogue/Collets/5C-Fixtures

kvom · « **Reply #12 on:** July 08, 2009, 04:39:37 PM »

Assuming you can clamp the bar on the mill vise and locate the center, then a bit of trig and the dials/dro will get you there.

websterz · « **Reply #13 on:** July 08, 2009, 05:12:28 PM »

Drill a 1/2" hole in the end of the hex to a depth of about an inch. Face it off nice and square and part it off in the lathe. Turn down and inch of the 1.5" round to a good press fit (again with a good square shoulder) and press (hammer, what have you) into the hex, which has just become an indexing fixture. Clamp the hex in the mill vise, supoport the round end with a v-block so it's level, drill, rotate, repeat. Piece o'cake.

shred · « **Reply #14 on:** July 08, 2009, 11:25:27 PM »

Can you tap one end? Then you could just run any reasonably accurate hex head bolt in tightly and clamp that in a vise.

NickG · « **Reply #15 on:** July 09, 2009, 04:58:13 AM »

I was going to suggest the same method Dave did using the chuck jaws. I've used this method a few times, infact I used it for my chuck back plate and it worked spot on.

I would scribe the circumference with a sharp tool as you said then scribe 3 lines crossing that circumference using the cross slide, indexing with each chuck jaw. Then transfer to mill or drill for drilling.

Nick

raynerd · « **Reply #16 on:** July 09, 2009, 01:04:24 PM »

Quote from: kvom on July 08, 2009, 04:39:37 PM

Assuming you can clamp the bar on the mill vise and locate the center, then a bit of trig and the dials/dro will get you there.

Kvom - was thinking about this a last night in bed (is that a bit sad?

)

NickG - that is a great idea - could then also check it with trig as a double check!

Hummm interesting - I was 90% sure I was going to purchase a RT this evening but you have made me think again now. I will get one, just ideally not this month.

kvom · « **Reply #17 on:** July 09, 2009, 04:58:45 PM »

If the trig i too challenging, then Machinery's Handbook has bolt circle X-Y formulas for any number of holes.

raynerd · « **Reply #18 on:** July 09, 2009, 05:50:28 PM »

Well I have given it ago but it has been a while since I did trig. last! I have expressed co-ordinates in terms of x, -x, y and -y from the centre point of the bar and expressed the answers in terms of d and therefore they should work with any pitch circle diameter that the holes are to be drilled at 120deg intervals.

You can hopefully see what I did from my workings below:

Hole 1
X= 0
Y= d/2

Hole 2
X= 0.433d
Y= -0.25d

Hole 3
X= -0.433d
Y= -0.25d

I haven`t a clue if it is correct, my dad seemed to agree with me which is a start!

I am curious to know how accurate this will be using the DRO on my mill!! Perhaps the opportunity for using it as a necessity for the first time!

Chris

DavesWimshurst · « **Reply #19 on:** July 09, 2009, 10:55:45 PM »

Looks good.

With DRO should be easy, without don't let backlash in your feed screws and having to read backwards for one of your feed directions trip you up.
Nice C-O-M!
Dave

M for math.

raynerd · « **Reply #20 on:** July 10, 2009, 06:59:23 AM »

Thanks for the verification - I`ll be giving it a go shortly and see how it works out! I have fitted my little X2 mill with the fignoogle DRO layout and so I`ll be using that - however they are only cheapo DRO bars so I`m not entirely sure how accurate it will be. I hope it is as accurate as a RT.... I`ll let you know how it goes.

Chris

NickG · « **Reply #21 on:** July 10, 2009, 07:01:02 AM »

That's right 10/10!

Stilldrillin · « **Reply #22 on:** July 10, 2009, 07:42:43 AM »

I used trig/ pythagoras almost daily, up to retirement.

Those figures jumped out at me!

They`re right!

You never forget...... Like riding a bike......

David D

bogstandard · « **Reply #23 on:** July 10, 2009, 08:08:26 AM »

Go to the downloads section here

http://madmodder.net/index.php?action=downloads;sa=view;down=3

1 Click on the program name and download it to your desktop.

2 Run it.

3 Choose Pitch circle diameter from the top menu.

4 Choose how many holes you want.

5 Select Imperial or Metric.

6 Put in the size of the circle in decimal, leave x and y centre coords as they are.

7 Press calculate.

Job done, 1 mins work.

Bogs

raynerd · « **Reply #24 on:** July 10, 2009, 08:48:55 AM »

Thanks guys - it has been a while since I did Trig, back when I did my A levels! I`m glad I calculated it right..

Cheers for the link, John - usefull tool.

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Author Topic: Drilling around the circumference without RT (Read 18810 times)

bogstandard