Spindle Drawbar Force Gage
We offer the Clamprite Spindle Drawbar Force Gage, spindle taper adapters and related tooling.
The Clamprite Spindle Drawbar Force Gage is the best selling tool for testing the spindle drawbar pull force of CNC Machining Centers. It is an economical spindle checking tool to maximize machine up time and to minimize machine down time costs.
Why Measure Spindle Drawbar Force, Spindle Drawbar Force Loss
Drawbar force is often the first thing to weaken or fail on a CNC Machining Center!
A stack of 100 to 150 Belleville springs provide the force that pulls the toolholder into the spindle taper. The Belleville springs wear into the drawbar and the friction between springs and drawbar can result in drawbar force loss, which can permit chatter, bad finish, reduced cutter life, and scrapped parts. Belleville springs can and do fatigue and break, resulting in extreme loss of drawbar force. Programmers will often compensate for this, unaware that one spring after another is failing.
The toolholder can eventually pull out during a cut, causing damage to the spindle taper, bearings, toolholder, cutter, and fixture. A routine force check with a spindle drawbar force gage would reveal drawbar force loss, and this is the cue that corrective action should be initiated.
How to Use the Spindle Drawbar Force Gage
By placing the Spindle Drawbar Force Gage in the spindle taper, and causing the drawbar to pull on the pullstud that you have threaded onto the internal transfer screw coupling, it takes less than one minute to check the drawbar pull force against the machine manufacturer's recommended level. It has no batteries, no cables and no delicate electronics to go wrong. A 3,000, 5,000 or 10,000 psi pressure gauge converts directly to pounds of force. Many shops use the Clamprite Gage and most say it paid for itself the first time they used it ... because they caught a drawbar exerting low force and they corrected it, before it caused a crash and cost a spindle taper regrind or a full spindle repair. Keep a running record of each spindle's measured drawbar pull, and be alerted to drawbar force loss and trends over time. The more often you check spindle drawbar pull, the sooner spindle drawbar force loss is detected.
To check if your drawbars still pull hard - Call: 519 671 3911 or email to our address at the page bottom !
Spindle Drawbar Force Gage - Gage Head, Spindle Adapter, Spindle Dawbar Force Gage Kit
Clamprite Gage Kits provide an easy, accurate and economical means of measuring tool clamping force. Kits are furnished in a foam fitted metal tool box and include the gage head, a spindle adapter, and an internal transfer screw coupling to accept all pull studs. You use your own pull stud.
The universal gage head fits to the various types and sizes of spindle adapters including:
CAT30, CAT40, CAT45, CAT50, CAT60,
BT30, BT35, BT40, BT45, BT50, BT60,
ISO30, ISO40, ISO45, ISO50, ISO60,
HSK-E25, HSK-E32, HSK-E40, HSK-E50, HSK-E63, HSK-A25, HSK-A32, HSK-A40, HSK-A50, HSK-A63, HSK-A80, HSK-A100, HSK-A125,
Capto C3, Capto C4, Capto C5, Capto C6, Capto C8, Capto C10,
NC5-46, NC5-63, NC5-85, NC5-100,
Kennametal KV4540, Kennametal KV5045, KM 40, KM 50, KM 63, KM 80
and other specials.
Select your kit by spindle(s) type and maximum drawbar force you will be testing. Order additional adapters from the list below:
CAT Spindle Drawbar Force Gage Kits (Gage Head and one or two Spindle Adapters)
- CG3K40C 3,000 lb gagehead includes CAT 40 taper adapter $829.00
- CG5K40C 5,000 lb gagehead includes CAT 40 taper adapter $829.00
- CG5K50C 5,000 lb gagehead includes CAT 50 taper adapter $849.00
- CG10K50C 10,000 lb gagehead includes CAT 50 taper adapter $885.00
- CG5K40/50C 5,000 lb gagehead includes CAT 40 & 50 adapters $989.00
- CG10K40/50C 10,000 lb gagehead includes CAT 40 & 50 adapters $1025.00
BT Spindle Drawbar Force Gage Kits (Gage Head and one or two Spindle Adapters)
- CG3K30B 3,000 lb gagehead includes BT 30 taper adapter $819.00
- CG3K40B 3,000 lb gagehead includes BT 40 taper adapter $829.00
- CG5K40B 5,000 lb gagehead includes BT 40 taper adapter $829.00
- CG5K50B 5,000 lb gagehead includes BT 50 taper adapter $849.00
- CG10K50B 10,000 lb gagehead includes BT 50 adapters $885.00
- CG5K40/50B 5,000 lb gagehead includes BT 40 & 50 adapters $989.00
- CG10K40/50B 10,000 lb gagehead includes BT 40 & 50 adapters $1025.00
ISO Spindle Drawbar Force Gage Kits (Gage Head and one Spindle Adapters)
- CG3K40I 3,000 lb gagehead includes ISO 40 taper adapter $769.00
Capto Spindle Drawbar Force Gage Kits (Gage Head and one Spindle Adapters)
- CG5K6CAP 5,000 lb gagehead includes Capto C6 taper adapter $1349.00
- CG10K8CAP 10,000 lb gagehead includes Capto C8 taper adapter $1549.00
CAT Spindle Adapters for Drawbar Force Checking
- CA40C CAT 40 Adapter $149.00
- CA50C CAT 50 Adapter $169.00
BT Spindle Adapters for Drawbar Force Checking
- CA30B BT 30 Adapter $139.00
- CA35B BT 35 Adapter $149.00
- CA40B BT 40 Adapter $149.00
- CA50B BT 50 Adapter $169.00
Capto Spindle Adapters for Drawbar Force Checking
- CA6CAP Capto C6 Adapter $695.00
- CA8CAP Capto C8 Adapter $839.00
All adapters include a Transfer Screw Coupling. A Transfer Coupling accepts all standard pull studs. You use your own pull stud. Special applications are also available.
HSK Spindle Adapters
- CHSK E25 Size E-25 Adapter $399.00
- CHSK E32 Size E-32 Adapter $419.00
- CHSK A40 Size A-40 Adapter $439.00
- CHSK A50 Size A-50 Adapter $469.00
- CHSK A63 Size A-63 Adapter $489.00
- CHSK A80 Size A-80 Adapter $679.00
- CHSK A100 Size A-100 Adapter $849.00
- CHSK A125 Size A-125 Adapter $989.00
HSK Spindle Drawbar Force Gage Heads for HSK Adapters
- CG3K 3,000 lb Gage Head $679.00
- CG5K 5,000 lb Gage Head for HSK E-25 to A-63 Adapter $679.00
- CG10K 10,000 lb Gage Head for HSK A-80 to A-100 Adapter $719.00
- CG15K 15,000 lb Gage Head for HSK A-125 Adapter $949.00
Note: HSK spindles must have at least 75% of original drawbar force to fully seat the arbors. HSK spindles need to be checked frequently to ensure there is sufficient drawbar force.
Frequently Asked Questions
1) I have various machines with drawbar force specifications up to 4600 Lbs. Can I use the 5000 PSI pressure gage for all the smaller, lower force machines too?
Yes. However, reading the numbers on the 3000 PSI pressure gage is easier than on a 5000 PSI pressure gage because there are fewer numbers on the dial. But a slight difference in reading accuracy is not that important because there is little concern about 10 or 20 Lbs -- or even 100 Lbs. The real concern is when a machine is 20% - 30% low on drawbar force. Spindle technicians usually accept 10% variation when rebuilding a drawbar.
2) What about the accuracy of the Clamprite Drawbar Force Gage versus the higher priced electronic and digital drawbar force gages? It is mentioned how the digital are “extremely accurate” in your sales brochure. Isn’t it better to have high accuracy when available?
Yes ... and no! More accuracy is good when FREE. We believe the electronic gages with digital display are overkill for the shop floor in terms of accuracy and cost. The extremely accurate and expensive digital drawbar force check gages are similar to what we use to certify the Clamprite Gage. Our accurate but rugged tool clamping force gage is better suited to a shop environment where the delicate electronic spindle drawbar force gages can be easily damaged. If a Clamprite Drawbar Force Gage is dropped, a pressure gage could cost $40. A digital gage can cost over $1,000 to repair. So, our Spindle Drawbar Force Gage can be purchased new for less than the repair cost of an electronic spindle drawbar force checking gauge with digital display. Incidentally, these digital drawbar force check gages are occasionally called a spindle drawbar dynamometer. Unfortunately, they neither measure power nor the two components of power ... angular velocity and torque. It simply checks and measures axial pull force ... there is no power to measure and a spindle drawbar force gage is no dynamometer.
3) My CNC Mill has a high speed HSK type spindle. Can I use the same gage head to test this machine?
Yes, the gage head used for testing the common long taper spindles is the same for testing the HSK spindle system. However, a special adapter is required for HSK spindle testing. These special adapters, available for all HSK spindle sizes, are very accurate, durable and low in cost.
HSK spindles must be tested frequently to assure that they are within 75% of spec at all times. The tool holders will not seat correctly if the drawbar is pulling less than 75% of spec. Besides higher drawbar force requirements, there are many more issues with the HSK system.
4) I can’t find the drawbar force for my machine anywhere in the manuals. Can you tell me what the drawbar force my machine should provide?
There are so many variations, even among very similar machines. Only the manufacturer can say for sure. Some general figures are: 1800 to 2500 Lbs for most 40-taper spindles, 3800 to 4800 Lbs for most 50-taper spindles except heavy-duty versions which may be considerably higher. This is only a reference, and not a guide for any specific machine or spindle. To obtain the specific force for any particular machine, get the model number, the serial number, and date it was built from the nameplate and consult the factory representative.
5) What is the difference between using a standard tool holder as the spindle adapter vs. using the specially designed Clamprite Spindle Adapters?
A standard end mill holder can be used as the interface for drawbar testing. Our Adapters cost less than most tool holders, and since there are no tool changer flanges, the 50 taper (one unit) adapter fits all CAT, BT, and ISO spindles. Finding the right holder can be time consuming because it is often back in use on a machine when it is needed.
But the best reason to use a Clamprite Spindle Adapter is because we have found tool holders to be out of tolerance to the gage line dimension of the spindle. In fact, some tool holders (from reputable manufacturers) were .0125 over the high tolerance limit. Some were nearly that amount below the low tolerance limits. This amount of variation can cause great differences in spindle drawbar force readings.
All Clamprite Spindle Adapters are inspected with spindle taper gages to verify gage-length accuracy. A spindle that has .001 wear on the surface will allow a tool to seat .0069 deeper into the spindle pocket -- well past the gage-line tolerance limits, and enough to cause reduced overall drawbar holding force!
6) I have a 50-taper spindle on a geared head machine designed for cutting steel. Can I use the 5000 PSI pressure gauge to test it?
Most 50-taper machines are below 5000 PSI, usually from 3800 to 4800 PSI. But some heavy duty 50-taper machines can go to 7800, or more. If you over pressure the gauge, it may become inaccurate. See precautions in the instruction manual. As a courtesy to our customers, Clamprite will replace a pressure gauge with another gauge at no labor cost, if shipping is prepaid both ways. The complete re-certifying procedure is done for a nominal fee of just $59.95 (includes certificate traceable to NIST).
7) One of our machines is very large and was designed for heavy duty use. Someone said it may provide over 10,000 Lbs of drawbar force. Can the CG be used to test its drawbar?
The Clamprite Gage II is a heavy duty version of the standard Clamprite Drawbar Force Gage. The standard Clamprite Drawbar Force Gage will test up to 10,000 Lbs when fitted with the proper pressure gauge. The Clamprite Gage II will test up to 15,000 Lbs. Contact us for testing of forces over 15,000 Lbs. If you attempt to test the spindle and it is over 10,000 Lbs, the 10,000 PSI pressure gauge may be ruined and hydraulic fluid may squirt out causing injury. See precautions in the Instruction Manual. Your gage head can be re-fitted with a higher reading pressure gauge at no charge if courier charges are paid both ways. There is a nominal charge for re-certification, recording and issuing a new certificate with traceability to NIST ($59.95).
8) Can a Clamprite Drawbar Force Gage fitted with a 10,000 PSI pressure gauge be used to test spindle with 2000 Lbs of force?
Yes, but reading a 3000 PSI gauge is slightly easier than reading a 10,000 PSI gauge because there are fewer numbers on the face of the pressure gauge but the 10,000 PSI gauge will show you the drawbar force that your machine is producing. Changing gauges should only be done by qualified hydraulic repair personnel. As a courtesy to our customers, Clamprite will replace a gauge with another one of different pressure at no charge, except for the gauge and re-certification. Labor is free. Use caution if you attempt replacement yourself, as the fluid can squirt out and cause skin irritation, and improper bleeding of the gauge and body may cause false readings. Also, commercial gauges can vary greatly in accuracy. Clamprite uses only high accuracy stainless steel pressure gauges, and we also test and certify each assembly for accuracy on a certified electronic test bench.
9) We are a small shop with no customer requirements to verify our drawbar force. How long can we go without checking or re-certifying the Clamprite Drawbar Force Gage.
A lot of attention is being given to machine condition today. Some companies, especially aerospace, are even condition-coding machines and requiring accuracy tests such as “ball-bar testing” to be performed by vendors before parts can pass QC requirements. It is just a matter of time before they realize that a drawbar is just as critical for consistent machining as the axis drives and ball screw condition. But under your circumstances, you might go a few years without worrying about the gauge accuracy. If the Clamprite Drawbar Force Gage is not over-pressured, it should remain accurate for many years. However, Clamprite will check the accuracy of your gauge for free as long as you own it, if shipping is paid both ways. We do not record and issue a new Certificate of Accuracy when doing a free courtesy check. But it will verify that your gage is still in the original condition. There is a nominal fee of $59.95 for a complete re-certification.
10) My machine uses hydraulic pressure to hold the tools in the spindle. Will the Clamprite Drawbar Force Gage work for this application?
Yes. Whatever the means of creating tool retention force, that force can be measured with the CG.
However, there is some confusion about this. Nearly all machines use the spring stack method of tool retention . But the method of releasing the tool from the spring pressure comes from a hydraulic piston which is usually energized by an air cylinder. Compressed air is supplied to the air-over-hydraulic piston (usually located on top of the spindle) which acts like a small jack-type press for compressing the spring stack which in turn releases the clamping force acting on the tool holder’s pull-stud. Sounds a little complicated, but is actually fairly simple once you have seen all the parts laid out. Sometimes people are confused about how the hydraulics work. The air-over-hydraulic piston can be heard during a tool change, but it is usually used to release the tools, not to hold them.
11) In advertising and in your Instruction Sheet you spell the word gauge as simply “gage” at times. Why the difference?
Gage (spelled this way) is somewhat traditional in the metal working trades, except when specifically discussing a pressure gauge. The bourdon-tube type of pressure gauge has come to be known as simply “a gauge“, whereas many other gages (like radius gages, depth gages, etc.) are more like a method of measuring. Most tool making companies like the L.S. Starrett Co. for example, still use the older spelling of gage when describing their products. Most dictionaries list both spellings as acceptable.
12) You used to offer an adapter to test drawbar force on a Bridgeport mill. Why test drawbar force on a manual machine?
The Bridgeport Adapter was designed to give people a way to see and feel the kind of force that can be generated simply by turning a screw with a wrench. Most people are surprised when they use the CG on a Bridgeport type mill. It shows that most people apply about twice the tool holding force than most 40-taper CNC Machining Centers when they are new! It was a real eye opener and a lot of fun, and it might have saved some Bridgeports from damage.