Do you test your machine drawbars?

[Astonlee]

I was recently in my friend’s cnc machine shop, when an operator came in to discuss which of three identical Bridgeport’s that they were going to use to machine some components.

He past a comment to me about the different between these machines performance, when they had consecutives serial number!

So I ask him how regularly did he test these drawbar clamping force, and I knew from the look on his face he did not check them, so I went and got my old Clamprite tester, and he was staggered by the results, which clearly show why the performance of his machine varied so much.

So I wondered how regularly do other check their spindles?

NB. You wouldn’t drive your car around with loose wheel nuts

[Rockyr49]

Since we repair spindle tapers, we check drawbar force on every machine possible. I've seen machines that had a force of zero on the gage and they still are running, complaining of finish problems. It is one of the most overlooked specifications. We recommend checking force every 6 months, or whenever there is any other repair being made. THe clamp-rite is a decent gauge for the price. You are mainly looking for a change in clamping force. Get a baseline and watch for any significant changes. We use a Command adaptive dynamometer which let's us check any size taper from 30 to 50. Keep an eye on those forces and the condition of the taper. Bell mouthing will occur over time and with a weak unattended drawbar problem it will happen faster. A tight drawbar and properly ground taper can make a night and day difference in operation of the machine.

Rocky
Spindle Grinding Service Inc

[kawazuki]

Never considered it - tool in, screw up drawbar to hold tool + another 1/2 a turn! In the absence of any specific guidance (for my machines anyway) my method could be under, over or spot on! And no I wouldn't drive a car with lose nuts - but I don't check them between tyre changes either!

[Astonlee]

Sorry kawazuki for the misunderstanding, this does not apply to drawbar on manual machines!

[Rockyr49]

Right. Only talking power drawbars here. Most really don't know how much force should be there. This week I fixed a taper and checked the drawbar on a Mazak 50 taper. It showed 600lbs. The customer thought that would be fine. Nope. Should be up around 4000lbs. Unless otherwise informed by the manufacturer, we like to see 2000lbs for a 40 and 4000lbs for a 50. Some are less, some are more.

[Astonlee]

According to my tester the drawbar tension is commonly 1800-2500 lbs (816-1134 Kg) of Force for 40 taper spindles, 3800-4800 lbs (1723-2177 Kg) for
most 50 taper spindles, and higher for heavy duty machines or larger spindle tapers. Drawbar force varies considerably from machine to machine, and they reccomend that you check the your machine manual.

[underthetire]

They never checked them here before I started. I own a Command digital set, but we bought the clampright one for here. The command is a lot nicer, but 3X the price. had some 40t ones at the 1K range. Scraped the machines since then (They were old Hurco's anyway). A drawbar check and repair is a lot cheaper than a spindle repair, drawbar repair, and a new tool holder.

[MTBA]

Here at Machine Tool Bearings & Accesories, we have a spindle rebuilding/repair facility. Most customers are unaware of the problems that a weak drawbar can cause for them. Many machines that are suddenly experiencing a problem with chatter and poor finish are found to be caused by weakening drawbar bellville washers. We use and recommend the Clamp-rite gauge because of the reasonable price and ease of use. Start by getting a baseline for all your equipment and then test (and record) monthly to see when changes are occuring. You can then use the data to inform you when to do preventive maintenance. Its interesting that the machine tool manufacturers put little emphasis on the importance of checking drawbar pressure, when it is so important to the quality of machining and the life of your spindle

[lwindrem]

I have not made a post because I could not Find a Place to do so.
Is this the pace to enter a post.

Best Regards , Lawrence C Windrem