increasing milling machine speeds.

[Dave CParticipant @davec87625]

I have just recently bought a Harrison Universal mill. The speeds of which are 45 – 1000 rpm Horizontal and then apparently 84 to 1860 when the vertical head is fitted due to internal gearing I presume. Apparently when new the machine came with two speed options, The second option being 67 – 1500 and 125 – 2800 with the vertical head fitted. The second would be the preferable option due to higher speeds however I have the slower one.

I would like to increase the speed on the machine to make it more usable with smaller cutters if possible, Information on the excellent Tony Griffiths site suggests that simply altering the pulley diameter at the motor and gearbox input shaft is the way it was accomplished.

The mill is single phase. I still have the original 3 phase motor.

1/      Is there any electrical way of increasing the speed ( excuse my electrical ignorance )

2/      Is the alteration of the pulley diameters the best option and if so any assistance on size icrease or location of relevant replacement pulleys would be greatly appreciated.

3/ At the current 1860 RPM with the vertical head fitted what would be the smallest usable milling cutter I could comfortably use.

The mill is solely for model enginering use.

Absolutely any advice as to the usability of my current speeds or upgrading would be greatly appreciated. ( I am a total novice to milling I may add ! ! )

Dave

[Dave CParticipant @davec87625]

[BogstandardParticipant @bogstandard]

Dave,

 

My machine goes up to 2000RPM electronically (stepless), but I normally use around 1500 RPM for1.5mm HSS cutters into free cutting steel with no problems at all. That is a bit slow on RPM, but I adjust my feed rate to compensate (at home, there is no rush to get things done).

 

If I wanted to get the speed right up, rather than modding the machine, I think I would consider a secondary cutting spindle for the small stuff. There would be no extra wear to your machine by running it a lot faster.

 

Years ago, I made something very similar for the toolpost on my lathe. That was before I could afford things like rotary tables and milling machines for doing small indexing work, and it worked very well indeed.

 

Auxilliary mill spindle

 

 

Bogs

[WALLACEParticipant @wallace]

Bigger pulley and belts to match is probably cheepest option – or if you’re swimming in cash, put back the 3 phase motor and run it on an inverter than can go higher that 50hz. (say 100) – that’ll give you double the speed). I know there are issues with cooling a motor designed to run at 50 hz at anything higher  – but if you’re not loading it fully (which I imagine you won’t be with small cutters) I wouldn’t imagine it’s a problem.

 

 

W.

 

* Always assuming your 3 pahse motor can run on 220v 3 phase otherwise it’s even more cash !

 

[KWILParticipant @kwil]

The cooling question more oftern arises with lowered speed because the motor spindle mounted fan is not blowing hard enough. Motor losses will be higher at 100Hz but not impossibly so.

[peter walton 1Participant @peterwalton1]

What is the spec of the single phase motor, if it is 4 pole you could fit a 2 pole motor and get double speed.

 

Peter

[John OlsenParticipant @johnolsen79199]

Running a motor faster will not usually cause cooling issues. There is generally a loss of torque, but this is not an issue with small cutters anyway.  Most controllers allow you to program the maximum speed. I have one in use here that allows me to go up to 200 Hz. I havn’t tried to go that far, but have run it up to 100 Hz often. The more serious issue is whether the motor is balanced well enough to go faster, and how much the bearings will stand. The University of Canterbury (New Zealand) did some checks on the locally made motors back in the 80’s, and found they were generally OK up to about 10,000 rpm, eg the bearings were rated for that speed and the balance was good enough as supplied to stand that. That would correspond to running a two pole motor up to 150 Hz, eg three times normal operating speed. You also need to consider the bearings in the machine as well. (For instance the plain bearings in the Myford ML7 should not be run too fast)

 

regards

John

[Billy MillsParticipant @billymills]

Dave,

You don’t say what size cutters you want to use. If you are  around or under 1/8″ then speeds of 5,000-20,000 might be needed depending on what you are cutting. That is why some mills have seperate high speed heads for vertical milling to replace the standard spindle. 

 

The forces are very much lower with small diameter cutters but the bearings of standard mills are not normally rated for anything like the speeds needed for small cutters.  One option is to get a high speed  Kress  head and mount that in place of the vertical head. The mountings can be a lot lighter than for full size cutters.

 

Regards,

Alan.

[Ian S CParticipant @iansc]

On the thread on tool post grinders wod working routers were mentioned, one of these could be the basis of a high speed head  similar to the one that Bogs made.Ian S C

[KWILParticipant @kwil]

I see ArcEurotrade are now selling high speed spindles, don’t know what they are like.

[Dave CParticipant @davec87625]

Thanks guys a whole load of information for me to take in there.>>

I have looked into an inverter which comes in at @ £450 then I have the installation to consider as the mill has a dial controlled power feed and also a light which all run through one 3 pin 240 volt plug at the minute. I would not know where to start should I attempt to wire that myself to be totally honest.>>

My mill came with two speed options when new with the highest being 1500 rather than the 1000 at the horizontal spindle which I have and up to 2800 through the geared vertical head. I would not; I don’t think want to exceed that too much but I feel confident the machine / bearings etc. would be able to cope as it was designed to take these speeds originally.>>

The pulley alteration throws up another problem as the gear box end has a clutch fitted which I would rather not tamper with and without altering the base the maximum motor pulley diameter possible would bring it up to the same diameter as the top one. An increase of some 30mm only.>>

Peter Walton suggests changing the motor to a 2 pole rather than a four pole if fitted? How can I tell by looking as I have no electrical knowledge at all.>>

As the original 3 phase motor has been removed and replaced with a single phase one it has occurred to me that the motor  speeds could well be different anyway so this would also give me a different speed to the one displayed on the levers of the machine ?>>

I have ordered a tachometer to establish exactly what RPM I am getting which I should have shortly.>>

Would the general opinion be that speeds of 1800 ish would be sufficient ? I do not expect to be using less than 3/32 dia for home use / model engineering. Looking at Tom Senior machines etc. they seem to have a similar speed.>>

I am starting to wonder if all the work to alter the speed would really  be  necessary .>>

> >

 

[,Participant @nousername29627]

Hi Dave

I Have exactly the same Harrison mill that you have (1860 rpm) and can use 1/16″ or 1.5mm FC3 cutters in mild steel ,brass, bronze and even aluminium with no problems. You have to take care obviousle and use very slow feeds. My auto feed motor is still 3 phase and that is driven from an inverter so I can slow the feed rate down to almost zero but I mostly use hand feeds with cutters of this size. I suggest you have a try before you spend money and time altering things and dont forget that all the figures for cutting speeds and feed rates that are published are for Industtry where time is money. If it is just home use like me then try it – at the end of the day you can buy a heck of a lot of cutters for the price of a new motor/inverter or even a set of pulleys

Phil

[Dave CParticipant @davec87625]

Thanks Phil

 

I think you may be right about leaving things as they are for a while and seeing how I go.

Its reassuring to know that you manage fine with the same machine and speeds.

Time to invest in some FC3’s and see how I cope first I think.

 

Many thanks

 

Dave

[John OlsenParticipant @johnolsen79199]

My Chinese vertical mill/drill does about 1600 at the fastest speed, and I have just been successfully cutting small T slots with it. These have a 1/16 inch wide vertical slot, and the T part is about 2.4mm wide. (Now I have offended both the imperialists and the metricists!) I use the highest machine speed, and set the feed to the slowest it will do. That way the cutter at least gets a steady feed, which I am not sure I could guarantee with hand feed. So these sort of speeds will work with small cutters. I only take small nibbles, I feed the 1/16 cutter down by about 0.25mm each pass.

 

It is funny to watch, thinking that if needed you could be ripping out a 16mm slot by 8mm per pass with a much higher feed rate!

 

regards

John

 

 

[John HaineParticipant @johnhaine32865]

That inverter price is way too high!  Look on http://www.homeworkshop.org.uk

 and look around, there’s a chap regularly selling them for much less.

[Dave CParticipant @davec87625]

As an update. I today got the tachometer and my vertical head is geared 1.1,

Therefore as feared my top speed for the vertical head is the same as the horizontal spindle  ! ! ! !

1000RPM ! !

Looks like the 3 phase inverter or a higher speed single phase motor may be the option I think.

 

Thanks for all the help and advice recieved

 

Dave

 

[John OlsenParticipant @johnolsen79199]

If you are going to be spending money, I would suggest putting it into an inverter rather than a single phase motor, as this will give you more for the money, eg variable speed as well as the higher speed. That is of course provided the three phase motor that you still have can be connected for 230 Volt working. Most of them can.

 

The GBP 450 for an inverter does sound a bit over the top. It is hard to compare directly, but I can get an inverter for a kW or so for about $300 NZ, that would be the equivalent of about GBP 150 at the moment. Bigger ones are dearer but not proportionately so. 

 

The wiring need not be too hard, you have a single phase motor in it at the moment, so the power feed to the inverter picks up from those existing connections. The inverter will have a control box with its own on/off and speed controls that connects to the terminals on the inverter. (The control box may be an optional extra, but you will need one.) That just has to be placed somewhere convenient for use. The three phase motor connects to three terminals plus earth on the controller. The wires all need to be appropriate to teh service, eg rated for the Voltage and current and suitalby protected for the environment. So it is not trivial, but need not require getting inside the machine and rewiring the other bits. The inverter wants to be mounted somewhere that will not get it covered in chips and cutting oil, and where it will not get too hot. You may still not want to do it yourself, if you are not familiar with such things, but it is the sort of thing that you might find a fellow club member to guide you with, if such is available.

 

regards

John

 

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