RPM for countersinking in mild steel

[rodw]

Hi guys, I just wondered if you can help me out here? It is a simple question, so please bear with me,

I have a part I make

It is pretty simple really. It is 100 mm x 32mm x 8mm mild steel. It has two holes. One is tapped to M8 and the other is countersunk for an M8 machine screw.

I started off building this from scratch out of 8mm x 32 mm bar stock but then I got a bit cunning and had it laser cut. This worked OK and then I got lazy and sent the whole job out 100 at a time and it came back finished and powder coated. The price went up so last time, I ordered 300 of them and went back to tapping and countersinking them on my drill press. So far I have finished 200 of them and have about 100 to go. For some reason in this batch, every now and again I hit a hard piece of steel and I have ruined a couple of countersinking tools (after making hundreds with my first one). I figured that somehow the steel has been hardened in the laser cutting process.

I tried an indexable countersinker for $33 but have ruined all 3 sides of the included cutter so I am not keen on buying $100 worth of inserts to continue down that path!

So anyway, I decided to finally do something serious with my mill and machined the jig I made years ago before I bought a lathe/mill. I was able to square the jig up so the sides held in the vice are parallel with the part and I indicated it in using an edge finder.

I cut one with a blunt countersink which lined up nicely and am going to buy another tool in the morning so my long winded question is:

"What is the ideal RPM for a countersink operation like this?"

Oh and in case you were wondering, I used a tapping tool in the drill press to cut the threads and it was easy as to thread the 300 holes.

 

[gus]

I use Japanese Three Flute Countersunk Drills. With M.S. I run drill at 100 rpm or lower with copious amount of brush applied Tapmatic Oil. The chips comes out smootly with no chatter marks. Same with counterbores.

 

[MuellerNick]

The countersink shown in one of the pictures is absolutely un-suited for countersinking. It is good for deburring.


Nick

 

[rodw]

The countersink shown in one of the pictures is absolutely un-suited for countersinking. It is good for deburring.


Nick

Nick, I had read that too but this one has proven to be the best of the lot I have used, it just carves it out. I tried a 3 flute one but it did not last long! I get confused with all this and I have spent a lot on this.

Gus, thanks, I think my low speed which i have set up on is about 160 but I do have a planetary gear I can fit which will halve that speed. I have not used it yet, maybe I should give it a go. I do use cutting fluid.

 

[gus]

Hi Rod,

Japanese Countersink tool 10mm shank x 20mm O.D. Been using since 1980 in Ingersoll-Rand Singapore Plant. My turner swears by it. He is given direct excess to hardware saleman/delivery man to order turning tools. Good man. Order just what he need and I check his verbal orders.Never excessive. Good man. He knows more about turning tools than me----the factory boss.

 

[MuellerNick]

The most common error when countersinking: Too little feed.
Then, some chime in and say "reduce RPM!". Wrong! Proper RPM for 16 mm (the outer diameter counts) countersinking in mild steel is 560 RPM for an uncoated sinker.
Use cutting oil and increase your feed. Make chips, not dust.

The one you have used, has no relief, so it more rubs than cuts. Good for deburring sheet metal.


Nick

 

[rcfreak177]

I'm with Gus on this one.
Here is a countersink tool set at Hare And Forbes, $77.00 incl GST

http://www.machineryhouse.com.au/D1061

Would not run these ones at 500+ rpm though, around 80-100 rpm will be fine.

As Nick said keep the feed up to produce light chips and plenty of cutting fluid, (Rocol maybe)

Baz

 

[gus]

I'm with Gus on this one.
Here is a countersink tool set at Hare And Forbes, $77.00 incl GST

http://www.machineryhouse.com.au/D1061

Would not run these ones at 500+ rpm though, around 80-100 rpm will be fine.

As Nick said keep the feed up to produce light chips and plenty of cutting fluid, (Rocol maybe)

Baz

Hi Baz,


Japanese C/sink not cheap.I paid S$15 for the posted 10mm shank CS.
$77 for a set of several seems reasonable. C/sink will chatter if not treat right. Some Tapmatic Oil application make C/sinking easier.

 

[rcfreak177]

Hi Gus,

Yeah they defiantly are not Japanese quality but a good set for a fair price,

my set has stood the test of time, found out the hard way that they chatter if not enough feed is kept on them, hard to stop once it starts.

(nice fish in you'r profile picture)

Baz.

 

[RolandMM]

RodW,
Interesting production run. I like the Severence 6 flute countersink. I would run it slow, 60 rpm, with a heavy feed. If you are using mild steel as you say, it cannot be hardened by a laser or any heat treatment without addition of carbon so that is probably not the problem. I would suggest the steel is a low grade remelt which is not consistent throughout the bar. I occasionally thread medium size pipe (10 ") for a local shop. It is not round and has spots that remain shiny because the spot is hard. It has the manufacturer stenciled in another language and the country in unknown to anyone in the shop. Going to a better steel would solve the problem but be more expensive.

If you can get steel without hard spots I suggest you try a form tap. It is better suited for production tapping.

Roland

 

[lensman57]

Hi,

It is probably a combination of too fast an rpm, too slow a feed and the wrong tool that has caused the work hardeneing effect. I suggest you experiment on some defunct stock untill you get the parameters right, is the steel hot rolled or cold rolled?

A.G

 

[rodw]

Thanks for all the advice and ideas

I'm with Gus on this one.
Here is a countersink tool set at Hare And Forbes, $77.00 incl GST

http://www.machineryhouse.com.au/D1061

Would not run these ones at 500+ rpm though, around 80-100 rpm will be fine.

As Nick said keep the feed up to produce light chips and plenty of cutting fluid, (Rocol maybe)

Baz

Baz, thanks, I started with a Hare & Forbes set which he one I pictured came from. It got a bit blunt after a few hundred so I bought a 3 flute Sutton one which cost about as much as the H&F set on its own. I ruined it so bought the set you have displayed and the one for this sized hole was also destroyed.

The most common error when countersinking: Too little feed.
Then, some chime in and say "reduce RPM!". Wrong! Proper RPM for 16 mm (the outer diameter counts) countersinking in mild steel is 560 RPM for an uncoated sinker.
Use cutting oil and increase your feed. Make chips, not dust.

The one you have used, has no relief, so it more rubs than cuts. Good for deburring sheet metal.


Nick

Nick, Thanks again for elaborating. the tool actually makes large flat chips and feeds very easy

RodW,
Interesting production run. I like the Severence 6 flute countersink. I would run it slow, 60 rpm, with a heavy feed. If you are using mild steel as you say, it cannot be hardened by a laser or any heat treatment without addition of carbon so that is probably not the problem. I would suggest the steel is a low grade remelt which is not consistent throughout the bar. I occasionally thread medium size pipe (10 ") for a local shop. It is not round and has spots that remain shiny because the spot is hard. It has the manufacturer stenciled in another language and the country in unknown to anyone in the shop. Going to a better steel would solve the problem but be more expensive.

Roland, thanks for that. I wondered if it was cr#p steel as I have had no problem before. Yes, this little project and all of the parts I make have paid for all of my tools. The finished product is a body lift kit for a Toyota Hilux 4WD. The kit lifts the body off the chassis by 50mm (2"). This part (well 4 of them) lowers the radiator back 50mm to centre it on the fan once the body is lifted. I also designed and have manufactured a splined extension for the steering shaft. There are a fair few components in it. Here is a photo of an early prototype.

I've tried to outsource a lot of the work but I can output as many of the plastic blocks in an hour on my heap lathe as you can on a CNC machine so while I can "earn" $90 per hour, I'm keeping that one.

The welded component, I now get laser cut and the 5 axis laser chamfers the SHS tube for the weld and the two parts clip together like meccano so it does not need clamping in position. Now I powder coat everything as it is not much more cost than the paint I was buying!

I sell these kits and a few other bits online on my website. Linky in my signature.

Any, back on topic, hopefully, I will sort something out today. I am still undecided about which tool to go with, the one I have been using or a 3 flute one. Maybe I will get some of each.

I found the 3 flute ones chattered a lot in my drill press. I thought part of the problem was that the tool was not centred on the hole. Now I have indicted it in on the mill which is more rigid than my "cheapie" drill press, hopefully that will fix a lot of the problems. I will find out later in the day I guess! I will take my time and play with feeds.

 

[gus]

Hi Gus,

Yeah they defiantly are not Japanese quality but a good set for a fair price,

my set has stood the test of time, found out the hard way that they chatter if not enough feed is kept on them, hard to stop once it starts.

(nice fish in you'r profile picture)

Baz.

Hi Baz,

Was a lucky nite.All of us took some fish home. Breakfast was expensive.S$3.00 per bowl plus S$70 tips/fine to the Traffic Police for parking along double white lines.All the fishos thought the police can't be there at 7am. Ha Ha. All four fishos paid S$73 each for their b/fast.Ha Ha ha
Hi Baz. Will be happy to take you out in my Albin 28.No worries.We won't get lost with ChartPlotter and AutoPilot. The inland Sea is very calm. See You,

 

[rodw]

Gus, I can see why you are one happy fisherman! I am not much good at it having grown up nearly 1000 km from the sea in a 15" rainfall region!

Anyway, I got some new countersink tools

Nick will be pleased to see which one I chose (one of Baz's $77 3 flute specials!)

I played around with feeds starting at 100 RPM or so and increased the feed a couple of times and I settled on around 400 rpm, mainly because it was too hard to change the belts on my little mill.

I have to say Nick knows his stuff. There was no comparison between slow and fast cutting. At 100 RPM, it was taking me about 2 minutes per piece, once I got the speed up to 400, this halved. Anyway, I had a productive afternoon in my sweltering shed!

I think slow speeds might be OK if you only have a couple of holes to do but when doing a production run, it does not cut the mustard!

Anyway while I was at the candy store getting my countersink tools, I ended up putting a deposit down on an AL320G lathe. This is also called an L141 and a CQ9332 around the globe. The lathe needs to come up from Sydney but at least I got to take the stand home. It'll probably be a couple of weeks before I get the lathe and in the mean time I can make up some adjustable feet from some 3/4" adjustable Rod I have here as my floor is not level.

This is quite an upgrade for me moving up to a 38mm spindle and power feed on the cross slide. Oh and no more belts (except to go between low and high range). This one has pick gears for threading but I have not done that yet anyway so I did not see lack of threading gears to be a major issue. Once I eventually get it installed and sorted out, I will sell the machine I have and see if I can buy a Seig X3 mill with the proceeds.

Thanks everyone for their help and advice.

 

[MuellerNick]

Be splendid with the cutting oil!
You can increase the feed. Suggested are 0.14 mm / revolution. Depending on how deep you have to countersink, you can calculate the time. 1 minute sounds way too long for me.


Nick

 

[Charles Lamont]

Then, some chime in and say "reduce RPM!". Wrong! Proper RPM for 16 mm (the outer diameter counts) countersinking in mild steel is 560 RPM for an uncoated sinker.Nick

What do you mean by "proper"?

 

[rcfreak177]

The most common error when countersinking: Too little feed.
Then, some chime in and say "reduce RPM!". Wrong! Proper RPM for 16 mm (the outer diameter counts) countersinking in mild steel is 560 RPM for an uncoated sinker.
Use cutting oil and increase your feed. Make chips, not dust.

The one you have used, has no relief, so it more rubs than cuts. Good for deburring sheet metal.


Nick

Thanks Nick,

I stand corrected.
Will try to run my countersink tools a bit faster in future.

Stuck in my way's I guess

Baz.

 

[robcas631]

Gus, I love the boat!

 

[robcas631]

Why not refer to drilling charts for RPM?

 

[rodw]

Why not refer to drilling charts for RPM?

Rob, could you provide a link to some metric tables? My reference bible has feed rates, but I get vastly different values from what Nick has quoted for 16mm holes. From a few sources, I got answere varying from 240 to 740 rpm. 240 is definitely too slow from my experience discussed in this thread.