Speed control for the BT

[Popeye]

In cleaning up and shuffling around my junk I came across a 10" sanding disk I bought ages ago for my old Craftsman TS. The saws RPM was too fast to use it. As I'm sure the BT's is.
Is the BT motor too heavy to use a router speed control on? Or am I just whistling in the dark? Sure could have used a stationary disk sander this afternoon. Pat

[cgallery]

This is an interesting question. I have one of those sanding disks, too. I actually put it on the saw and turned it on once. Wow! I couldn't find the power switch fast enough. :-O

My previous saw was an old Sears belt-driven unit that I had used the sanding disk with on occasion, and it worked fine. What is the suggest RPM range for these sanding disks? And how many RPM's does the BT3K run?

And those router speed controls, how much do they allow you to slow a motor?

Thanks,
Phil

[LCHIEN]

This is an interesting question. I have one of those sanding disks, too. I actually put it on the saw and turned it on once. Wow! I couldn't find the power switch fast enough. :-O

My previous saw was an old Sears belt-driven unit that I had used the sanding disk with on occasion, and it worked fine. What is the suggest RPM range for these sanding disks? And how many RPM's does the BT3K run?

And those router speed controls, how much do they allow you to slow a motor?

Thanks,
Phil

From a theoretical point of view,
Answers to your questions
Electronic Speed controls work only with Universal motors, and yes the BT3x has a universal motor, sot its possible.

The BT3x turns somewhere around 4500-5500 RPM depending upon load, then unloaded like a disk sander free spinning, the speed will be near the maximum. I think in calculations of diameter and rotational rate, the outer edge will be moving at around 120 mph which is roughly 180 feet per second or nearly 11000 Feet per minute. That would be way too fast for sanding, IMHO. It will burn or be hard to control.

My 6" disk sander turns at 3400 RPM which roughly works out to 2800 fpm at the edge. If that is the ideal sanding speed then you need to slow down the BT to 25% of the original speed.

I'm not 100% sure that the speed controllers work that low. They work by means of phase angle conduction control. You'll have to try it and see, but I'm not real hopeful.

[Popeye]

Well,...... it works. Used the HF speed control and it dropped the speed down to nothing. Haven't tried sanding yet, I have the metal disk but no sanding sheets for it. Pat

[Tamarack]

Well,...... it works. Used the HF speed control and it dropped the speed down to nothing. Haven't tried sanding yet, I have the metal disk but no sanding sheets for it. Pat

That's great news, I had been thinking of getting a speed control for a single speed 13 amp PC router I have plans to mount in the accessory table on my BT3100. With one of those sander plates and my shopvac hooked to the dustport on the BT, my sanding chores will get easier to live with.
Paul

[cgallery]

These speed controls can't shorten the life of the motor, can they?

I would like to use my sanding disk, but not at that price.

And how do they affect the power of the motor?

Still there Loring? :-)

Thanks,
Phil

[LCHIEN]

These speed controls can't shorten the life of the motor, can they?

I would like to use my sanding disk, but not at that price.

And how do they affect the power of the motor?

Still there Loring? :-)

Thanks,
Phil

Yeah, I can't see that it would be deleterious to the motor.
Popeye says it works but, my concern is that the system is "open loop" so that there is no constant speed control like there is on the expensive variable speed routers with feedback electronic control. Since the speed is partly a function of the load, a slow running speed controlled motor MIGHT come close to stalling whem you applied the load. These router speed controllers I THINK work best when controlling motors under a constant (e.g. unchanging) load and when loaded in the upper half of the speed range. I think you may just have to try and see if its satisfactory turning 25-50% and doesn't slow too badly when you apply the load.

One good thing about a big 10" disk is that the linear speed (in feet per minute) will be proportional to the distance from the center. To sand less aggressively apply the sanding closer to the center and more aggressively move to the downturning side of the disk. I'm not sure which side of the disk you apply the sandpaper - I assume there's got to be a hole for the arbor to penetrate so you can mount the arbor nut and the paper has to have a hole in it. I'm thinking it would be on the Left side of the saw and you would stand on the left of the saw facing the disk to use it. Then the BT-mounted disk would turn clockwise, the opposite direction of most disk sanders I have used which rotate counterclockwise.

I'm sure you all know how important it is that you apply the workpiece on the down-going side of the disk and Never the upgoing side as it will lift the piece and fling it.

I'm kind of thinking here that the power must be proportional to the speed, that is if you run at half speed then only half the full rated power will be available, and that's because the conduction angle is limited. That would probably explain why the performance at low speeds is not that great. Popeye got his to turn real slow with no load but I'll bet it had no torque to speak of.

Probably the thing to do is get a parted out BT with just the motor and arbor half length rails and an auxiliary table (for the left side), change out the pulleys to a v-groove type set with a final speed around 1000-1200 RPM and replace the belt with a link-belt) put in the sanding disk and make a no-speed control needed dedicated sanding station out of it.... An excuse for some of you to buy a third BT!

As a disclaimer this is about 75% theoretical and about 25% experience-based (but I am 100% sure about sanding on the down-going side!), so it might be worth a try just to see what you get. A disk attachment is around $20 or less and you may already have a "router" speed control or can get one for around $10-13, not a huge investment and Pat (Popeye) is all set up anyway.

[vaking]

I want to agree with Loring on practically everything he said and add a little.
Firtsly, I just checked that standalone 10" disk sander is rated for 1750rpm no load and 3/4 HP. BT3100 I believe is rated for 4800rpm no load. That means in order to use it for sanding you need to reduce speed between 2 and 3 times.
From the power perspective - most speed controllers are rated for 15Amps, many big routers are rated for 15 Amps and so is BT3100, so speed controller seems like a good fit for BT3100. I have a speed controller from MLCS, I never tried it with BT but I used it with my rotozip. I never needed to slow down a rotozip as a router but I once used the rotozip witn plunge base to drill some holes ( the eternal question of drilling true vertical bench dog holes). Drilling holes at 30000rpm was too much fun, so I used the speed controller to reduce the speed. It worked well except for very low speeds when speed became visibly unstable and jerky. I am sure at that time the speed was definitely below 500rpm, which means that speed controller was well usable at 1/3 of normal speed. For sanding operation speed stability and accuracy is probably not critical. Going back to power, BT3100 is somewhere around 2 HP (some say 1.5, others claom 3HP) , if you reduce speed 2 - 3 times and presuming that power is reduced proportionally you still get around 3/4HP so BT3100 with speed controller should work fine as a 10" disk sander. Also BTW, Freud sells a special "calibration and sanding disk" and abrasives for it. Here is the link
http://www.amazon.com/gp/product/B00...lance&n=228013
People are saying this disk is good to have even if you don't plan to use it for sanding.

[LCHIEN]

I want to agree with Loring on practically everything he said and add a little.
Firtsly, I just checked that standalone 10" disk sander is rated for 1750rpm no load and 3/4 HP. BT3100 I believe is rated for 4800rpm no load. That means in order to use it for sanding you need to reduce speed between 2 and 3 times.
....

Just a warning:
(Don't mean to be critical or nit pickey but its a saftey thing)

if the BT3 no load speed IS 4800
and the disk no load RATED speed (e.g. maximum) is 1750 then you want to run it somewhat (like 10%) LESS THAN 1750 so you should slow the BT by 1/3 (1600 RPM) or SLOWER (which would be like 1/4th, or 1200 RPM).
not between 1/2 and 1/3 as you suggest.

I stick by my suggestion of 1/3 or 1/4th speed.

Note that's the same reason you should run a 5500 RPM or better rated blade on the BT3x which runs at 4800 RPM. Safety factor, y'know.
Just to scare you a little the centripetal forces acting on a spinning object are proportional to the sqauare of the diameter. A 10" spinning disk has about four times the rotational inertia, momentum and forces acting on it than a 5" disk spinning at the same speed.

I would tend to agree that 1/2 HP should be plenty for a sander, even that big a diameter.
You're only removing the top layer, altho abrading not cutting.

[Sawatzky]

Phil had the question I have. I had asked about using a speed controller on the PC 690LR. Most say it is okay, but I am afraid that it will burn out the motor because Porter Cable told me not to use one for that reason. I have been leary ever since about speed controllers on universal motors. But most of you seem to think it is okay. So, I asume that speed controllers pose no threat to universla motors of any type, right?

[LCHIEN]

Phil had the question I have. I had asked about using a speed controller on the PC 690LR. Most say it is okay, but I am afraid that it will burn out the motor because Porter Cable told me not to use one for that reason. I have been leary ever since about speed controllers on universal motors. But most of you seem to think it is okay. So, I asume that speed controllers pose no threat to universla motors of any type, right?

well, how many types of universal motors are there? are there types of types?
PC probably just want to sell you a VS unit. You know they don't want to take responsibility if anything goes wrong (oh, but you said it was OK).
I bet they tell you that you should only use porter cable bits with that router, too, if you asked them.

The biggest problem is the loss of power/torque. you might tend to overload the motor running at lower speeds but heavy loads. This could possibly cause problems.

[vaking]

I want to say that concern about speed controller reducing life of a motor for a router is grossly overrated in my opinion. Please remember the chart of best router speed vs size of a bit. For a bit less that 1-1/4" diameter the speed controller should not be used because full speed for that size is best. For me the use of bits larger than that is not frequent. If you do use a lot of large bits - you ought to get yourself one of those 3 HP routers and they all have variable speed. For an occasional use I would not worry much.

[Stytooner]

I have heard that you shouldn't use them with soft start motors for some reason. I'm sure you wouldn't want to hook one up on a unit that already has VS capability. I have only used mine just a few times, but it worked well then and I can't see anything detrimental that it caused. One thing toremember is that torque is definately decreased relevant to the decrease in speed. Depending on the application, it can still work well with slower feed in reduced power situations.

[Sawatzky]

Good. Now I can use a router speed control and not really worry about hurting anything.

[JimD]

I have used a router speed controller for a long time on the older of my two PC690s and on an old Ryobi R-500 router that is semi-permanently in my router table. I have built a lot of raised panel doors spinning horizontal panel raising bits 3 inches or a bit more in diameter with the router slowed with the speed controller. Speed control is a bit subjective - there is a scale but no easy way to calibrate it - but otherwise I see no problems. Judging only from the sound of the router, I would say that the controller has some sort of circuitry in it to increase current when the router is under load. It sounds like the speed starts to fall off and then comes back.

I have used a sanding disk on the BT3100 as I said in another post at full speed. You need to use low force but I had no problem with it. It will also burn if you do not use low force. I didn't think of using the speed control. I do not see why it would be an issue.

My PC690 used to get hot when I was doing this work but I think it was because I was sucking the air out of the router table from the bottom and pulling against the cooling fan of the router. I do not check on the Ryobi often when doing this but probably should. I have the router table sucking from the top of the lift which makes the DC assist the Router fan instead of fighting it. I don't think it gets hot but then I haven't really been checking. I would suggest anybody concerned check the motor temperature (i.e. is it hot to the touch?) as an indication if the motor life is being shortened.

Jim