# Table Difficulty Factor (TDF) for measuring table "toughness"

#### JC

##### Coos Cues
Gold Member
FYI, I've added the following to the table difficulty factor (TDF) resource page, for easy future reference:

from Sloppy Pockets in AZB post, concerning how to properly measure the pocket mouth and throat dimensions (at the intersections of the yellow lines, not at the labeled red dimensions):

Thanks again,
Dave

Hmm. I need to go home and check my table now because that pocket in the photo is not the same pocket I measured for my BU exam. It says 3 1/2 in that photo which I took when I first assembled the table last year but the pocket at the other end of the table I measured for BU was 3 7/8 across the same points at the throat. After analysis I think they pocket angles are likely the same since the pockets play real consistent but Donny may have cut the facings slightly shorter at the back on the larger measurement one which would not affect table play as it's beyond the shelf and the ball is gone by then. Looking at the lines in the diagram of sloppy pockets and using a little algebra just measuring on the screen I can see my PAF is actually 1.10 which puts my table difficulty at 1.1x.98 or 1.078 rounded up to 1.08. This variable of measurement could be eliminated by just measuring the angle of the pocket instead of the throat and plugging that in instead. Harbor freight has just the tool for 3 bucks for those who don't have the capability. http://www.harborfreight.com/multipurpose-angle-finder-1028.html

JC

Last edited:

#### iusedtoberich

##### AzB Silver Member
Silver Member
I caught up with the whole thread.

I have a vast amount of measuring experience, from a lifetime of woodworking, and more recently, metalworking.

I think it is extremely difficult to measure the theoretical corners of the mouth of the pocket, as per sloppy pocket's diagram.

Those theoretical points are in thin air. You need to hold two of them in your mind, while holding a ruler over both of them. I just tried doing this, and was not satisfied with my results.

I also have a sliding bevel gage. If I had two of them, and 3 hands, I might have better success obtaining this theoretical measurement.

I will look into this further. Perhaps something like laying post it notes stuck on the cushion can extend the lines of the cushion to a real intersection point, that can then be measured to and from.

#### dr_dave

##### Instructional Author
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Silver Member
I like the finer divisions. I was going to suggest this as things progressed, but I'm glad don't need my help figuring things out.:thumbup2:

Why not add them across the entire range, though? If you listen to the pros, there is a definite difference between the way 4 1/8" pockets play compared to 4 1/4" pockets. Since most tables today have pockets between 4" and 4 1/2" across the throat, this range would seem to me to be the one that needs the finest gradations.
Good suggestion! FYI, I've added more divisions.

Regards,
Dave

#### dr_dave

##### Instructional Author
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My table
8'
4 1/4" mouth
4" throat
1 1/2" shelf
.91 TDF

- Andy
I get the following:

67tbird -- 8':0.90 -- 4 1/4":1.05 -- 1/4":0.94 -- 1 1/2":0.98 -- 0.87

Please check me again. You might have done you calculation before the most recent changes (or I might have made a mistake).

Thanks,
Dave

#### dr_dave

##### Instructional Author
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Silver Member
Random thoughts:

Perhaps it would be good to measure all the pockets on a given table, (since there may be variances from pocket to pocket) then add them up and use the averages...

Perhaps a degree of "difficulty" should be added if the cushion facing vertical angle is less than say 14 degrees...(15 or more being easier?)
Those are excellent suggestions. If I were to add any new factors, these two things would definitely be at the top of the list. But to keep things as simple as possible, while still capturing the most important factors, I decided to leave them out for now. It is difficult enough to correlate everything already with only four factors. Also, I would still like to better understand why the vertical (draft) angle is so important. What is going on with a 10 degree angle vs. a 15 degree vertical (draft) angle? The horizontal pocket-wall angle effect is clear in how it causes a ball to rattle out, but I still don't understand the vertical-angle effect. Can anybody explain it convincingly?

Thanks,
Dave

#### dr_dave

##### Instructional Author
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Silver Member
The thing about the bonus ball table for pros is that once your aiming gets to a certain level of precision and consistency, pocket size is no longer as important as how it accepts balls. Take those 3 and 7/8 pockets and give the facings 144 degrees and add a half inch of shelf and they do not become "a bit harder", they become a pin ball machine.
I agree that the level of the player makes a big difference in table comparisons. However, I don't want to add a "player ability" factor to the equation. I only want to include easily-measurable and well-understood effects directly related to table and pocket geometry.

Good point, though,
Dave

#### 67tbird

##### AzB Silver Member
Silver Member
Dave, I had different shelf and PAF values, I must have used outdated charts. Thank you for the correction.
- Andy

Sent from my C771 using Tapatalk 2

#### dr_dave

##### Instructional Author
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Silver Member
... This variable of measurement could be eliminated by just measuring the angle of the pocket instead of the throat and plugging that in instead. Harbor freight has just the tool for 3 bucks for those who don't have the capability. http://www.harborfreight.com/multipurpose-angle-finder-1028.html
I agree it would be better if we had direct and accurate angle measurements, but I decided at the beginning to require only a single ruler (no other tools or devices). With decent mouth and throat measurements, the implied angle is accurate enough, certainly within the margin of error of this semi-subjective system.

I do plan to improve the drawing in my document so it will be much clearer how to measure the mouth and throat dimensions more carefully and accurately.

Dave

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
I caught up with the whole thread.

I have a vast amount of measuring experience, from a lifetime of woodworking, and more recently, metalworking.

I think it is extremely difficult to measure the theoretical corners of the mouth of the pocket, as per sloppy pocket's diagram.

Those theoretical points are in thin air. You need to hold two of them in your mind, while holding a ruler over both of them. I just tried doing this, and was not satisfied with my results.

I also have a sliding bevel gage. If I had two of them, and 3 hands, I might have better success obtaining this theoretical measurement.

I will look into this further. Perhaps something like laying post it notes stuck on the cushion can extend the lines of the cushion to a real intersection point, that can then be measured to and from.
If people want to be this accurate (which would be nice), I love your post-it note idea.

Good suggestion,
Dave

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
Here's the latest update after the most recent changes (which had only small effects):

Data reported by AZB users in table difficulty factor (TDF) order, based on the table size factor (TSF), pocket size factor (PSF), pocket angle factor (PAF), and pocket shelf factor (PLF):

name -- TSF -- PSF -- PAF -- PLF -- TDF
tough 10' -- 10':1.10 -- 4":1.15 -- 3/4":1.02 -- 1 7/8":1.03 -- 1.33
example "B" -- 9':1.00 -- 3 7/8":1.20 -- 5/8":1.00 -- 1 7/8":1.03 -- 1.24
Bonus Ball -- 9':1.00 -- 3 7/8":1.20 -- 1/8":0.97 -- 3/4":0.98 -- 1.14 (Bonus Ball table)
rexus31 -- 9':1.00 -- 4":1.15 -- 3/8":0.98 -- 1":0.98 -- 1.10
FatBoy -- 9':1.00 -- 4":1.15 -- 1/4":0.97 -- 1":0.98 -- 1.09
TATE -- 9':1.00 -- 4":1.15 -- 1/4":0.97 -- 7/8":0.98 -- 1.09
Qaddiction -- 9':1.00 -- 4 1/8":1.10 -- 5/8":1.00 -- 1 3/8":0.99 -- 1.09
cigardave -- 9':1.00 -- 4 1/2":1.00 -- 3/4":1.02 -- 1 3/4":1.00 -- 1.02 (typical Pro-Cut Diamond)
SloMoHolic -- 9':1.00 -- 4 3/8":1.02 -- 5/8":1.00 -- 1 3/8":0.98 -- 1.00
"standard" table -- 9':1.00 -- 4 7/16":1.00 -- 9/16":1.00 -- 1 5/8":1.00 -- 1.00 ("standard")
Sloppy Pockets -- 8'+:0.95 -- 5":0.95 -- 1":1.10 -- 1 3/4":1.00 -- 0.99
JC -- 9':1.00 -- 4 7/16":0.98 -- 9/16":1.00 -- 1 3/8":0.98 -- 0.96
12squared -- 9':1.00 -- 4 7/8":0.95 -- 3/4":1.02 -- 1 1/2":0.98 -- 0.95 (typical Gold Crown)
MSchaffer -- 9":1.00 -- 5 1/10":0.90 -- <3/4":1.02 -- >1 3/4":1.03 -- 0.95
rexus31 friend GC -- 9':1.00 -- 4 1/4":1.05 -- 1/4":0.94 -- 15/16":0.95 -- 0.94
mamics -- 9':1.00 -- 4 9/16":0.98 -- 5/8":1.00 -- 1 3/16":0.95 -- 0.93
Neil -- 7':0.85 -- 4 1/8":1.10 -- 5/8":1.00 -- 1 3/8":0.99 -- 0.93
BRussell -- 8':0.90 -- 5":0.95 -- 13/16":1.05 -- 1 1/2":0.98 -- 0.88
67tbird -- 8':0.90 -- 4 1/4":1.05 -- 1/4":0.94 -- 1 1/2":0.98 -- 0.87
Dopc -- 8':0.90 -- 4 1/2":1.00 -- 3/4":1.02 -- 1 1/4":0.95 -- 0.87
dr_dave -- 8':0.90 -- 4 3/4":0.98 -- 5/8":1.00 -- 1 3/8":0.98 -- 0.86
example "A" -- 8':0.90 -- 5":0.95 -- 1/2":0.98 -- 1 3/8":0.98 -- 0.82
Valley "bar box" -- 7':0.85 -- 4 1/2":1.00 -- 0":0.94 -- 3/4":0.95 -- 0.76 (typical Valley/Dynamo "bar box")

#### Mr. Bond

##### Orbis Non Sufficit
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Silver Member
Also, I would still like to better understand why the vertical (draft) angle is so important. What is going on with a 10 degree angle vs. a 15 degree vertical (draft) angle? The horizontal pocket-wall angle effect is clear in how it causes a ball to rattle out, but I still don't understand the vertical-angle effect. Can anybody explain it convincingly?

Thanks,
Dave

I suppose a good place to start would be to look at how the contact point changes, as the angle of the facing increases or decreases, and what effect that change of contact point would have during impact...

would not a higher contact point tend to produce more downward force on the average ball...?

#### iusedtoberich

##### AzB Silver Member
Silver Member
The precision in peoples abilities to take a measurement, due to pocket corners that are rounded, holding imaginary points in your mind, parallax, inexperience with measurements, and probably other factors, need to be factored in the charts, imo.

For example, I don't think I can measure using a single ruler within 3/16" on all the measurements you are asking for. I am extremely experienced with measurements. I own and use tools to measures down to .0001" (tenths), and the more common woodworking scales that are graduated in 8ths through 64ths.

I think you went the wrong way, having "more" graduations in your chart. 1/8" graduations when someone like myself can't hold 3/16" measurements just doesn't jive. Its like a cop's radar gun being graduated every 1mph, and your speedometer graduated every 20mph. You'd have no chance avoiding a speeding ticket. I'd almost make the minimum graduation on the pocket opening 1/2".

nominal 3.5"
nominal 4.0"
nominal 4.5"
nominal 5.0"
nominal 5.5"

Have the user just try to pick the value closest to the nominal. If it seems right in the middle between two of the nominal values, go with the tighter pocket. This could also potentially eliminate the need to distinguish between theoretical cushion corners and actual rounded off cushion corners.

#### rexus31

##### AzB Silver Member
Silver Member
I'm still a believer that cloth type needs to be factored in as well.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
The precision in peoples abilities to take a measurement, due to pocket corners that are rounded, holding imaginary points in your mind, parallax, inexperience with measurements, and probably other factors, need to be factored in the charts, imo.

For example, I don't think I can measure using a single ruler within 3/16" on all the measurements you are asking for. I am extremely experienced with measurements. I own and use tools to measures down to .0001" (tenths), and the more common woodworking scales that are graduated in 8ths through 64ths.

I think you went the wrong way, having "more" graduations in your chart. 1/8" graduations when someone like myself can't hold 3/16" measurements just doesn't jive. Its like a cop's radar gun being graduated every 1mph, and your speedometer graduated every 20mph. You'd have no chance avoiding a speeding ticket. I'd almost make the minimum graduation on the pocket opening 1/2".

nominal 3.5"
nominal 4.0"
nominal 4.5"
nominal 5.0"
nominal 5.5"

Have the user just try to pick the value closest to the nominal. If it seems right in the middle between two of the nominal values, go with the tighter pocket. This could also potentially eliminate the need to distinguish between theoretical cushion corners and actual rounded off cushion corners.
I don't think you are giving people enough credit.

Some people have reported measurements to within a 1/16" and even thousandths of an inch (although, that is a bit extreme, IMO).

I think that with a little care, a simple ruler (with 1/16" division), an improved diagram (which I hope to create soon), and your Post-It note idea, people can easily be accurate to within 1/8" (or even a 1/16").

Regards,
Dave

#### cigardave

##### Who's got a light?
Silver Member
I'm still a believer that cloth type needs to be factored in as well.
It definitely has an affect.

Without cost being a consideration, we tend to select the cloth for our table based on which game we typically play.

For me, it's rotation games so I went with Simonis 860.

For a 14.1 player, he would likely pick Simonis 760.

We can (somewhat) readily change the cloth on our home tables... likely based on the cost and the game that we typically play. It's a variable that we control as table owners without a huge investment... unlike paying a table mechanic to extend our subrails, thereby tightening up our pockets.

#### cigardave

##### Who's got a light?
Silver Member
I think that with a little care, a simple ruler (with 1/16" division), an improved diagram (which I hope to create soon), and your Post-It note idea, people can easily be accurate to within 1/8" (or even a 1/16").

Regards,
Dave
Dave,

I need to re-measure my "typical Pro Cut Diamond" using the post-it note idea. I'll try to do that tonight.

#### iusedtoberich

##### AzB Silver Member
Silver Member
I don't think you are giving people enough credit.

Some people have reported measurements to within a 1/16" and even thousandths of an inch (although, that is a bit extreme, IMO).

I think that with a little care, a simple ruler (with 1/16" division), an improved diagram (which I hope to create soon), and your Post-It note idea, people can easily be accurate to within 1/8" (or even a 1/16").

Regards,
Dave

Those measurements within 1/16" don't prove anything. The proof in the pudding would be to have that same person measure your table, and then have you measure their table, etc. This is a very common scenario when trying to get reliable measurements. The persons taking the measurement can lead to a LOT of variation. Its not discrediting the person, its just the way it is. There really is a lot of skill in taking measurements. Add to that complication in our case of pool tables, we have theoretical points we are trying to measure to.

I'll keep quiet now, except to say that whatever modification you come up with, please try it yourself several times, and have a few people you know also try it and see if you get the same results. Its silly to revise something every 5 minutes, and then to recalculate all the numbers each time as well.

I'd also be happy to try out a few methods on my table that might make measurements easier with just household items.... but it will have to wait a couple of weeks, I'm going on vacation

#### dr_dave

##### Instructional Author
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Silver Member
Dave,

I need to re-measure my "typical Pro Cut Diamond" using the post-it note idea. I'll try to do that tonight.
Sounds good.

Thanks,
Dave

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
Those measurements within 1/16" don't prove anything. The proof in the pudding would be to have that same person measure your table, and then have you measure their table, etc. This is a very common scenario when trying to get reliable measurements. The persons taking the measurement can lead to a LOT of variation. Its not discrediting the person, its just the way it is. There really is a lot of skill in taking measurements. Add to that complication in our case of pool tables, we have theoretical points we are trying to measure to.

I'll keep quiet now, except to say that whatever modification you come up with, please try it yourself several times, and have a few people you know also try it and see if you get the same results. Its silly to revise something every 5 minutes, and then to recalculate all the numbers each time as well.

I'd also be happy to try out a few methods on my table that might make measurements easier with just household items.... but it will have to wait a couple of weeks, I'm going on vacation
Your points are well taken. And I agree that people need to be very careful when interpreting the diagram and taking measurements at the table. They should also use Post-It notes on the "points" at both the mouth and throat, and a piece of paper under the pocket "points" (looking as straight down as possible and/or using a T-square or any square-box item). I think that with care, people can easily get within an 1/8" on all measurements. Even if they can, the results will still be within the margin of error for the rough and approximate table-difficulty factor (TDF).

Thanks again for your input, and I look forward to whatever advice you come up with to help people take more accurate measurements.

Have a great vacation,
Dave

#### Mr. Bond

##### Orbis Non Sufficit
Gold Member
Silver Member
Those measurements within 1/16" don't prove anything. The proof in the pudding would be to have that same person measure your table, and then have you measure their table, etc. This is a very common scenario when trying to get reliable measurements. The persons taking the measurement can lead to a LOT of variation. Its not discrediting the person, its just the way it is. There really is a lot of skill in taking measurements. Add to that complication in our case of pool tables, we have theoretical points we are trying to measure to.

I'll keep quiet now, except to say that whatever modification you come up with, please try it yourself several times, and have a few people you know also try it and see if you get the same results. Its silly to revise something every 5 minutes, and then to recalculate all the numbers each time as well.

I'd also be happy to try out a few methods on my table that might make measurements easier with just household items.... but it will have to wait a couple of weeks, I'm going on vacation

I hear what you're saying, but, I think that the actual measurements matter less than the theoretical association they have. In other words, its a scale of 'relativity' that you can plug your own numbers into, which means that each individual can only trust the accuracy of their results as far as they can trust their own ability to measure.