RPM for single point cutter?

[Bill Alston]

I don’t have an ornamental lathe but would like to try something like the image below. It was done with a single point cutter mounted in the head stock but I’m wondering if I could use one of my routers mounted on a compound table instead. I’m thinking though that a router, even on its lowest speed is too fast for a single point cutter. Thoughts?

 

[Bill Alston]

I think I’ve found an answer to my own question, together with an alternative solution. The minimum speed on my router is 11,500 RPM. This type of cutter has a maximum recommended RPM of 12,000 so should be suitable for making the small shallow cuts I intend to take. I’m pretty sure these kinds of speeds are too high for a single point cutter.

 

[RichColvin]

If I read your advertisement correctly, the cutter is ~2” in diameter.

Comparing this to the use of a dado blade on a table saw, the dado blade would spin around 3,400 rpm. Maybe you can compare an 8” blade run at 3,400 rpm has the same surface feet/minute at the cutter as a 2” blade running around 13,600 rpm. But that is scary to me.
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Keyway cutters on milling machines are also similar. The recommended surface feet/minute for these on plastic is 200 (https://internaltool.com/docs/reference/saf-keyway-cutters.pdf). That equates to a 2” cutter spinning at

200 ft/min * 12 in/ft / (2 * pi in/rev) = 389 rpm

Note: I welcome any input a machinist may have for this.
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The drilling charts say that a 2” Forstner bit should be revolved at 500 rpm. Other large cutters have similar speed recommendations when drilling.
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It seems to be well balanced, but it will still be cutting only a small part of the rotational circle; Maybe only 10° of the circle, leaving 350° spinning in the air.
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Regardless, I believe that running this cutter at 12,000 rpm will be too fast and probably unsafe.

If I were to use such a cutter in a drilling spindle on my rose engine, I’d run the bit at a speed around 200-500 rpm.

 

[Bill Alston]

Thanks for your input Rich. I don’t disagree with you but the linked cutter is designed to be used in a router and as far as I can tell none of them I’ve seen run any lower than 10,000 RPM. The description does also state a maximum of 12,000 RPM. I think I may beg the question on a wood working forum to see what the general consensus is. Failing that I’ll contact one of the router manufacturers to see what they say. I do agree though, that cutter does seem pretty large for those kind of speeds. I have seen even larger ones though!

 

[Tim Hunter]

I would not hesitate at all to run that cutter at 12,000rpm.

Tim

 

[Bill Alston]

Thanks Tim.

 

[Gerald Lawrence]

If you are determined to use a router use a straight bit

 

[Bill Alston]

If you are determined to use a router use a straight bit

Wrong orientation for what I want to do.

 

[Richard Coers]

If you are determined to use a router use a straight bit

The end of a straight router bit will not provide a smooth enough surface for ornamental turning.

 

[Darryl Fective]

Wrong orientation for what I want to do.

But will a router bit like that give you enough depth? At some point, wou;dn't the base of the router interfere?

 

[Bill Alston]

But will a router bit like that give you enough depth? At some point, wou;dn't the base of the router interfere?

That did occur to me. The router I’m using is quite slim but I need to take some measurements to see how far down a box I can cut.

This is the type I have. I’m having trouble finding a 43mm mount in the UK at a reasonable price, I may have to make my own.

 

[colinsp]

I use a cutter just like that in my drilling frame and have run it at various speeds up to the maximum of my drilling frame of 8000 RPM. On Box wood and African Blackwood I have found the higher RPM's give a better cut with a slow rotation speed of the Rose Engine.

 

[john lucas]

I think people have answered your question. The problem is the router bits that might do this won't extend down far enough to more than Maybe 2 rows. You can but metal working fly cutters but they typically come in 3/8" or 1/2" shanks that won't fit the smaller trim routers.

 

[Bill Alston]

I think people have answered your question. The problem is the router bits that might do this won't extend down far enough to more than Maybe 2 rows. You can but metal working fly cutters but they typically come in 3/8" or 1/2" shanks that won't fit the smaller trim routers.

Much depends on the size of cutter. I’ve just measured the nose of my router and using a 6mm wide cutter I can get at least 8 rows.
With a 5mm cutter maybe 10. For something like Box, or another fine grain timber that can take fine detail, I’d like to use these sort of size cutters.
It will be a while before I can try it as I still need to get a compound table which will likely need some modifications. And of course it looks like I’ll need to make a motor mount. I already have some material for that, just a matter of finding some time.

 

[colinsp]

With a 3mm cutter I have done 11 rows and could have done more but I was using a CNC motor with an ER11 collet chuck. If making a box you can always do the carving on the lid separately from the base of a box. This is a Boxwood box made with the 3mm cutter. The other photo shows the cutter and motor on my Rose Engine.

 

[Bill Alston]

With a 3mm cutter I have done 11 rows and could have done more but I was using a CNC motor with an ER11 collet chuck. If making a box you can always do the carving on the lid separately from the base of a box. This is a Boxwood box made with the 3mm cutter. The other photo shows the cutter and motor on my Rose Engine.

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That looks nice Colin, and the 3mm looks really good. I might have to revise my cutter sizing. I did think about a spindle motor but they seem quite expensive and run at a high speed.
I’ve been looking at a long nose electric die grinder but can’t seem to find a low speed version. Most of the are 25,000 to 33,000 rpm.

Edit: Colin, how many steps did you make on that box, 24?

 

[colinsp]

That looks nice Colin, and the 3mm looks really good. I might have to revise my cutter sizing. I did think about a spindle motor but they seem quite expensive and run at a high speed.
I’ve been looking at a long nose electric die grinder but can’t seem to find a low speed version. Most of the are 25,000 to 33,000 rpm.

Edit: Colin, how many steps did you make on that box, 24?

Bill

I have 2 3 and 4 mm cutters that I got from Wealden. Excellent quality and not too expensive. The motor I got from Aliexpress https://www.aliexpress.com/item/1005004522599165.html and it wasn't too expensive. It is variable speed so you can slow it down to a very low rpm. Yes it was a 24 peak rosette.

 

[Bill Alston]

Thank very much for all that Colin, much appreciated.

Edit: have you seen these Colin, I spotted it when I first started looking at this type of cutter a few days ago.

 

[colinsp]

Bill, no I haven't seen those but have used both straight cut and ball end router cutters with some success.

 

[Bill Alston]

What compound table are you using Colin?

 

[colinsp]

I am using a Chinese one from Vevor with a rotating base similar to this one https://www.aliexpress.com/item/33010042213.html It did need a bit of clean up before use.

 

[Kevin Jenness]

With a 3mm cutter I have done 11 rows and could have done more but I was using a CNC motor with an ER11 collet chuck. If making a box you can always do the carving on the lid separately from the base of a box. This is a Boxwood box made with the 3mm cutter. The other photo shows the cutter and motor on my Rose Engine.

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It seems to be working at the minimal cut depth shown but I would be cautious running a 2" diameter bit on a 1/4" shank with that much extension from the collet. Many bits, such as the one shown in post #2 above, have a maximum extension marked on the shaft for a reason.

 

[colinsp]

It seems to be working at the minimal cut depth shown but I would be cautious running a 2" diameter bit on a 1/4" shank with that much extension from the collet. Many bits, such as the one shown in post #2 above, have a maximum extension marked on the shaft for a reason.

I don't use the one in post#2 I use an alternative which is smaller in diameter and it is inserted the correct length for an ER11 collet.

 

[Tim Hunter]

If you want more axial reach, run the cutter in an electric die grinder.

 

[Bill Alston]

If you want more axial reach, run the cutter in an electric die grinder.

I’ve been looking for one, they even do long nose versions. Sadly most of them run at 25,000 to 30,000 rpm. A motor speed controller might work to slow it down? but adds to the cost.

 

[Kevin Jenness]

Not inexpensive, but this is a good quality long nose variable speed die grinder with a 1/4" collet. Makita 7-28k rpm grinder

 

[Tim Hunter]

'plenty of variable-speed die grinders available.

 

[Bill Alston]

Not inexpensive, but this is a good quality long nose variable speed die grinder with a 1/4" collet. Makita 7-28k rpm grinder

That looks good. Not cheap at £240 though, and as it’s 110 volt I’d need to buy a site transformer, another £110.
Thanks for the heads up though, I’ll have another look again.

Edit: I’ve found a 240V at £260. I don’t have that kind of money for something that won’t be used very often.

 

[colinsp]

Bill, put 'CNC spindle motor' into Amazon. There are various at lots of different prices. Most use an ER11 collet chuck so you can use Dremel cutters and 1/4" router cutters and the reach is sufficient for most boxes without danger.

 

[Bill Alston]

Bill, put 'CNC spindle motor' into Amazon. There are various at lots of different prices. Most use an ER11 collet chuck so you can use Dremel cutters and 1/4" router cutters and the reach is sufficient for most boxes without danger.

I did look at those but most of them seem to spin too fast. I’ve also seen some 8mm shank cutters I’d like to use.
The variable speed Makita die grinder with 8mm collet is the best bet - just too expensive. I’ll try my router once I get all the other bits.

 

[colinsp]

I did look at those but most of them seem to spin too fast. I’ve also seen some 8mm shank cutters I’d like to use.
The variable speed Makita die grinder with 8mm collet is the best bet - just too expensive. I’ll try my router once I get all the other bits.

Don't forget that all of those come with a variable speed so you can reduce from the maximum. I use one with no issues.

 

[Bill Alston]

Thanks again Colin. I’ve noticed that I could get a larger collet Chuck to fit the spindle on that motor.
I’m having a problem sourcing a suitable table at the moment. I’ve seen a 300 x 140 that would do the job nicely but the delivery cost is over twice that of the table!

 

[colinsp]

Bill, keep your eye on Facebook Marketplace or eBay for a s/h one. Amazon delivery can be very reasonable but the cross slide can be more expensive but cheaper in the long run.

 

[Bill Alston]

I’ve ordered a small compound table. I’m hoping I can make a larger table for it if it’s worth the effort. I won’t know until it arrives but I have the tools if it is.

 

[Bill Alston]

Colin, I’m not sure if this is of any interest but I’m part way through my router jig and remembered I bought a small collet Chuck with an 8mm shaft to use as a short extension in my router. I gave it a quick spin today to see what it was like and it seems ok. I just grabbed the nearest lump of wood, donned a face shield and spun it up. Only made a few cuts but It seems to work ok. The cutter is as far into the chuck as it goes if anyone is wondering. I don’t think I’ll need the extension very often but it’s there if I do.
More work to do on the jig, including a clear plastic (PETG) cover to shield the cutter.

 

[colinsp]

Bill, That looks good to me, you may want to seat the cutter a little deeper into the ER11 collet unless it has a particularly long shaft. With the ER11 collet you can get smaller ones and the use Dremel carbide cutters and also small CNC machine cutters usually 1/8" or metric equivalent. I take shallow cuts and increase the depth as I go rather than taking a big bite for additional safety. I also stand out of the line of fire at all time just in case.

 

[Bill Alston]

Bill, That looks good to me, you may want to seat the cutter a little deeper into the ER11 collet unless it has a particularly long shaft. With the ER11 collet you can get smaller ones and the use Dremel carbide cutters and also small CNC machine cutters usually 1/8" or metric equivalent. I take shallow cuts and increase the depth as I go rather than taking a big bite for additional safety. I also stand out of the line of fire at all time just in case.

Thanks for the additional info Colin. The cutter is as far into the collet as it will go.

 

[Bill Alston]

I finished the jig the other day so I thought I’d make a holder for a single point cutter. I really didn’t think this would work but I spun it up on the lowest speed on my router and it seems fine. I was expecting there to be a bad vibration. Test 2 will be trying it on some timber. It will be handy if this works as I’ll be able to grind my own profiles in HSS blanks. The one in the picture is 4mm diameter.
I also made a jig block for holding the cutters for shaping/sharpening on my belt grinder.

 

[Bill Alston]

Ok, I can wrap this thread up now. The first test with some Yew went well. I’ll be trying to source some Box and African Blackwood at some point.