Thread: Need help with mill bit/s

RHS typically has a weld line protruding somewhat on the interior. Best to make sure that seam is always on a side, you certainly don't want it on the bottom.

My experience with creating reasonably accurate top and bottom holes through RHS is that you need a rigid well clamped set up and that RHS isn't always square.
Probably best to do trials on RHS offcuts before you get too hung ho, see if the holes you can provide at minimal tooling expense are acceptable to your customer.

For this job I would be thinking of a hole saw to remove the bulk of the material.
Depending on the quality of the fit required for the 16mm rod, the cheapest and easiest options are either a 5/8" (15.875mm) drill bit which may flap around enough to give you the required hole size or a 16mm drill bit which will probably drill a little over 16mm but which may provide an acceptable fit.
Use the drills at the lowest speed you have with plenty of cutting oil.

Moving up the expense/expertise chart you come to a shop bought reamer, a home made D bit reamer or a boring bar.

Originally Posted by BobL

This was my point a few pages back.

Before the OP does drilling he needs to measure the 16 mm rod in a number of places as not all 16 mm rod is 16.00 mm and neither is it all uniform, and then we need to know the tightness of fit required.

Reaming from 15.5 to 16 mm is hard work given you have so many to do.
In these cases I have used a 5/8" (15.875mm) drill which makes reaming the last 0.125mm a LOT easier.
BUT we have to know the bar size and fit required.
Then you must test the 5/8" drill as it may still make a hole that exceeds the spec you need for the rod.

Spot on with everything you say regarding the type of rod being used BobL although bright bar is pretty consistent in size and ovality, albeit the diameter is always a thou or two undersize. Black bar on the other hand will be all over the place.

I think you and I have a different slant on reaming a 16.0 dia hole. A good HSS machine reamer will have no problem removing 0.5mm but we both know the 15.5 drill will drill oversize by about 0.1. My suggestion of using a 39/64" is the way to go but do H & F carry imperial sizes any more? Using a 5/8" drill & then reaming ... no way IMO but just the 5/8" drill might give the correct size for the bar being used.

Originally Posted by Snapey

Spot on with everything you say regarding the type of rod being used BobL although bright bar is pretty consistent in size and ovality, albeit the diameter is always a thou or two undersize. Black bar on the other hand will be all over the place.

I think you and I have a different slant on reaming a 16.0 dia hole. A good HSS machine reamer will have no problem removing 0.5mm but we both know the 15.5 drill will drill oversize by about 0.1. My suggestion of using a 39/64" is the way to go but do H & F carry imperial sizes any more? Using a 5/8" drill & then reaming ... no way IMO but just the 5/8" drill might give the correct size for the bar being used.

That's why I said the 5/8" needs to be tested.

Originally Posted by Snapey

I think you and I have a different slant on reaming a 16.0 dia hole. A good HSS machine reamer will have no problem removing 0.5mm

I think that it will have a lot of problems with the mill that the OP has. That machine would struggle to develop enough torque to pull the skin off of a dish of custard. Plus it has a sacrificial plastic gear in its train.

The question I haven't seen answered yet is - just how close does the pin/hole fit actually have to be? What's the purpose of all of this?

I'd probably do as you suggest, use an inch drill bit for a close clearance fit and call it done. If the fit needs to be better than that than it's most likely the pin(s) need turning to ensure consistent diameter anyway.

PDW

Thanx for all the advice peoples.

I'm sorry for not making it clearer.

A piece of 50mm RHS 4mm wall thickness.
6 x 16mm holes drilled through it top and bottom, 100mm apart
A 1000mm length of black bar with a collar 100-120mm up from one end is dropped into each hole. So approx 900mm or so protudes above the RHS
In the vertical wall of the RHS, not the weld-line side, a 1/2" BSW nut is welded on and the thread tapped through the RHS as well.
Then a 1" x 1/2" BSW set screw with case hardened teeth bites into each 16mm bar.


At this point it is hoped that the the tops of the 6 bars will be 100m apart, give or take a mill.

The bar is acceptably straight. I've rolled lengths of it on my plate. It measures 16mm on my old army mitutoyo vernier, battle scarred veteran that it is. But tomorow I will sand the bar and mic it.

Whew.

Now we know you're using black bar and a 1/2" bolt to hold it in place then there's really no need for a perfect hole. A 16 mm drill will do or even a 41/64" for a bit of clearance ... reduced web too.

As a set up you're best to use a vice and mount a location pin to pick up the hole you just drilled but 100mm away.

Thanx to everyone for all the help here.

Originally Posted by BaronJ

Hi Danny,

A blacksmiths drill is simply an ordinary drill with a reduced size shank so that it will fit into a standard 1/2" inch drill chuck. They are quite cheap over here and go up to 1 inch in size in 1/16"th inch steps. They will easily drill a hole 4" inches deep.

The reason that I said to use a pilot hole is that the drill web is quite thick, particularly on the big ones. A 5 mm pilot hole simply removes the need to apply a large amount of force to make the web cut metal. Also a 5 mm drill is long enough to go through both sides of your tube in one operation as is a blacksmiths drill.

This was the option I went with and no problems. I bought a 5/8 and a 16mm bit, just in case the 16mm was too sloppy. But I never needed to use the 5/8. A few hones with a rat tail file, and a flyshit skim on the little lathe and the pins fit like gloves.

Originally Posted by PDW

I think that it will have a lot of problems with the mill that the OP has. That machine would struggle to develop enough torque to pull the skin off of a dish of custard. Plus it has a sacrificial plastic gear in its train.

It had no problems at all drilling with the 16mm bit. I just put it in low gear and dialled up 480rpm. I hand fed slowly, and it just walked through.

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I bought this 16mm bit for the job. $31.50

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It worked fine. Almost. I never meant to road test it and analyse the results. It just so happened that when it died I had the figures at hand. I tried to work out what went wrong and if it was my fault. I'm unsure of my reasoning, what does anyone on here think?

The bit drilled 122 x 16mm holes through 4mm box tubing. That's a total of 528mm through mild steel. 480rpm x slow hand feed.

At this point the bit was still razor sharp. But the pilot bit (5mm) that passed down through the top wall of the tubing didn't always perfectly locate drilling through the bottom wall. This caused the 16mm bit to bind somewhat at times high up on the shaft. Also swarf from the bottom hole was being picked up and ground on the top wall.There are pictures of this binding.

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This caused no damage to the drill that I know of. The drill continued to work fine long after the tubing drill holes were finished. So I ruled it out as the cause of death

Now I had to use the bit to drill plugs of 21mm shaft. Each plug about 40-50mm long. For the first two-three plugs the bit waltzed through the 21mm bar. 480rpm slow hand feed. I only have a little tiny Sieg 3 lathe.

By about the 4-5 plug I was starting to have problems. The drill bit was binding in the plug. My first thought was that particular plug must be off centre. But it wasn't. I proved it by inserting the 5/8 back up drill into the lathe which continued the hole absolutely fine, though a flyshit smaller than I need. So I ruled it out as the cause of death

The drill appeared perfectly sharp, but I gave it a light hone anyway which you can see in the pictures. But that didn't solve anything. (The pictures make it look like I've changed the angle of the faces, but that's illusion. The hone I gave it is perfectly in line with the original edge)

Next I mike'd the clearance flutes, but they are 16.00 on the mike.

There is no burning or drag marks on the shank, so that's not the cause of death either.

The only thing I'm left with is that the clearance flutes have gone blunt. The proof is that the plug heats up instantly with the 16mm bit, but no heat at all with the 5/8".

The drill bit has only been used in the Mill and the Lathe, never in a drill press or a hand drill.

What do you think? Should the drill have lasted longer than 600-700mm of mild steel? Or am I expecting too much for $31.50?

The company places a lifetime warranty on this bit provided it's used fit-for-purpose. The rep calls into Kingaroy Equipment Sales all the time.

Should I take it back, or have I had a fair run for my money?

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Don't be fooled by the 'coarseness' that the high magnification produces. The drill bit is super sharp and will still drill fine. It just won't go in at any depth. (some of these pics you can click on more than once and they will grow larger)

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If you look carefully at the first photo in post 40, you will see that the very tips of the cutting edge have been knocked off. Your speed was fine although perhaps some lube would have been good. I would not take it back though - they would call that normal wear and tear.

If you sharpen it all the way to the tip it will live again.

Michael

Hi Greg,

There is very little cutting in the centre of the drill, this is one reason that I suggested drilling a pilot hole first.
You can grind the tip to reduce the core size and then regrind as a four facet drill. Basically on your drill the point has to rub the metal away so that the rest of the edge can cut. This makes it very hard to drill a large hole because of the amount of pressure needed to get the drill to cut. Use a pilot hole with large drills !

As an aside and basing the AU dollar at two to the pound, here in the UK that drill is a quarter of that price. I purchased a 1" inch blacksmiths drill about four weeks ago and it cost me £7.95p inc VAT. Not the same manufacturer of course but still made in China.