Tool Bit Cutting Speeds

[JonnyAlpha]

Hi,

I have have started to modify a BMC A Series Cylinder Head. The head is Cast Iron and I would like to confirm the correct cutting speeds for various tool bits.

I am using a Clarke Professional Air Die Grinder, which has 4 speeds from 8300RPM to 25000RPM @ max 90PSI.

I have a selection of mount point bits, some that were kindly donated by a professional head modder and some that I bought.

Of these I have been advised that the pink stones are hard, vitrified bonded pure
carborundum and the grey stones are aluminium oxide.
The burrs are Tungsten Carbide 'Chip Breaker Cut'.

I have also bought a set of Kennedy Aluminium Oxide mount points and these Aluminium Oxide mount points.

What I would like to know is the optimum cutting speeds for these different tools on cast iron and aluminium, or where to find the info?

Materials summary:
1. Hard Vitrified bonded pure carborundum
2. Aluminium Oxide
3. Tungsten carbide Burrs

Many thanks

 

[piman]

Hello Jonny,

do the suppliers not have this information to hand? At least cast iron is quite easy to work, but using those carbide cutters on harder materials may need less than the slowest speed on your grinder.
Aluminum is difficult as it clogs stones and burrs. If you want to do a lot of aluminium I would suggest going to the supplier for the correct grade of stone for aluminum. I do tend to spray WD40 on burrs when using them on aluminium to minimise clogging.

Alec

 

[grim_d]

Hello Jonny,

do the suppliers not have this information to hand? At least cast iron is quite easy to work, but using those carbide cutters on harder materials may need less than the slowest speed on your grinder.
Aluminum is difficult as it clogs stones and burrs. If you want to do a lot of aluminium I would suggest going to the supplier for the correct grade of stone for aluminum. I do tend to spray WD40 on burrs when using them on aluminium to minimise clogging.

Alec

Carbide burrs should be used at high speed, slower speeds kill them pretty quick particularly on stuff like steel. You'd need a pretty big burr to be running less than 8krpm. (>16mm).

There are burrs with the correct geometry for aluminium though I've never had the pleasure.

 

[brightspark]

this is the best shape cutter to have. its cone shaped and can start to cut at the small end and work your way up without it chattering i use them on stainless and whatever material i want at high speed if u have an air die grinder you can start off slow then let it have it. i use https://www.thomas-graham.co.uk/ind...garryson-9700-tc-ball-nose-tree-burr.658b9700

 

[piman]

Hello Grim,

did you note the minimum speed of 25,000 rpm?

Just had another look and there may be a typo as the maximum given is 8,300. I don't know which is incorrect. certainly 25,000 is too high for carbide and hard materials. Although I use my electric die grinder a lot I forget the speed range it has.

Alec

 

[JonnyAlpha]

Hello Grim,

did you note the minimum speed of 25,000 rpm?

Just had another look and there may be a typo as the maximum given is 8,300. I don't know which is incorrect. certainly 25,000 is too high for carbide and hard materials. Although I use my electric die grinder a lot I forget the speed range it has.

Alec

Which bit are you referring to ref speeds? Here is an extract from the Amazon listing for the same Die Grinder:

• 4 speed setting air regulator 8300-25000 RPM, Supplied with 1/8", 1/4" and 6mm collets

Hello Jonny,

do the suppliers not have this information to hand? At least cast iron is quite easy to work, but using those carbide cutters on harder materials may need less than the slowest speed on your grinder.
Aluminum is difficult as it clogs stones and burrs. If you want to do a lot of aluminium I would suggest going to the supplier for the correct grade of stone for aluminum. I do tend to spray WD40 on burrs when using them on aluminium to minimise clogging.

Alec

The Conical Norton Saint Gobain Aluminium Oxide bits on the Cromwell Site just state a maximum speed of 25000RPM.
The 5 piece Kennedy Aluminium Oxide state maximum RPMs of 33000 - 70000 for the various shaped bits.

 

[Kram]

Your points, the pink ones are corundum(ruby)/aluminium oxide with the grey being carborundum/SiC. I prefer the pink on ferrous. Grey are for harder steels?


The burrs with the "correct" geometry for aluminium look more like endmills and I wouldnt want to be holding when they grab. Ive never had a problem with clogging but soak then in hot lye for a few minutes to get them clean.

I really hate how burrs can grab, shatter, or skate accross your part destroying the finnish. Also had more than a couple of parts thrown from my grip and across the garden.

Higher speeds are less grabby, smaller burrs grab with much less force, so more controllable, so I generally stick to 6mm size.

this is the best shape cutter to have. its cone shaped and can start to cut at the small end and work your way up without it chattering i use them on stainless and whatever material i want at high speed if u have an air die grinder you can start off slow then let it have it. i use https://www.thomas-graham.co.uk/ind...garryson-9700-tc-ball-nose-tree-burr.658b9700

I have this 12mm 9700 and it scares me. I have no plans on chucking it in die grinder again. Slow speed abuse in the cordless...

 

[grim_d]

Hello Grim,

did you note the minimum speed of 25,000 rpm?

Just had another look and there may be a typo as the maximum given is 8,300. I don't know which is incorrect. certainly 25,000 is too high for carbide and hard materials. Although I use my electric die grinder a lot I forget the speed range it has.

Alec

Maximum of 25k, minimum of 8.3k on that pneumatic die grinder.

It's entirely dependent on the diameter and geometry (cut) of the burr itself. Speeds and feeds.

For a 3mm carbide burr 25k is well within appropriate speed.

For a 12mm carbide burr you might be down as low as 10k depending on application but I run mine way, way faster with no issues.

Your points, the pink ones are corundum(ruby)/aluminium oxide with the grey being carborundum/SiC. I prefer the pink on ferrous. Grey are for harder steels?


The burrs with the "correct" geometry for aluminium look more like endmills and I wouldnt want to be holding when they grab. Ive never had a problem with clogging but soak then in hot lye for a few minutes to get them clean.

I really hate how burrs can grab, shatter, or skate accross your part destroying the finnish. Also had more than a couple of parts thrown from my grip and across the garden.

Higher speeds are less grabby, smaller burrs grab with much less force, so more controllable, so I generally stick to 6mm size.

I have this 12mm 9700 and it scares me. I have no plans on chucking it in die grinder again. Slow speed abuse in the cordless...

Are you using a pneumatic grinder?

Too easy to slow them down and as such, dig in and grab.

I've switched over to a cordless DeWalt die grinder and it has so much torque I simply cannot (perceptibly) slow it down, it just does not grab, at all.